Portable locator system with jamming reduction

ABSTRACT

A portable self-standing electromagnetic (EM) field sensing locator system with attachments for finding and mapping buried objects such as utilities and with intuitive graphical user interface (GUI) displays. Accessories include a ground penetrating radar (GPR) system with a rotating Tx/Rx antenna assembly, a leak detection system, a multi-probe voltage mapping system, a man-portable laser-range finder system with embedded dipole beacon and other detachable accessory sensor systems are accepted for attachment to the locator system for simultaneous operation in cooperation with the basic locator system. The integration of the locator system with one or more additional devices, such as fault-finding, geophones and conductance sensors, facilitates the rapid detection and localization of many different types of buried objects.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/551,651, which was filed Oct. 20, 2006, and which is pending as ofthe filing of this application.

This application claims priority benefit under 35 U.S.C. §119(e) and§120 of the filing date of provisional Patent Application No. 60/730,124filed on Oct. 24, 2005 of Mark S. Olsson et al. entitled “Self-StandingMapping Sonde and Line Locator Employing Improved Display Methods withIntegral Ground-Penetrating Radar and Other Detachable DetectionApparatus.” The entire disclosure of said provisional application ishereby incorporated by reference.

This application is related by common inventorship and subject matter tothe commonly-assigned patent application Ser. No. 10/268,641, which wasfiled on Apr. 15, 2004 and published on Apr. 15, 2004 as U.S. PatentApplication No. 2004/0070399A1 entitled “Omnidirectional sonde and linelocator,” and the commonly-assigned patent application Ser. No.10/308,752, which was filed on Dec. 3, 2002 and published on Apr. 15,2004 as U.S. Patent Application No. 2004/0070525 A1 entitled “Single andMulti-Trace Omnidirectional sonde and Line Locators and Transmitter UsedTherewith,” both of which are entirely incorporated herein by thisreference.

This application is also related by common inventorship and subjectmatter to the commonly-assigned patent application Ser. No. 10/956,328filed on Oct. 1, 2004, the commonly-assigned patent application Ser. No.11/054,776 filed on Feb. 9, 2005, the commonly-assigned patentapplication Ser. No. 11/106,894 filed on Apr. 15, 2005, thecommonly-assigned patent application Ser. No. 11/184,456 filed on Jul.19, 2005 entitled “A Compact Self-Tuned Electrical Resonator for BuriedObject Locator Applications,” and the commonly-assigned patentapplication Ser. No. 11/248,539 filed on Oct. 13, 2005 entitled “AReconfigurable Portable Locator Employing Multiple Sensor Arrays HavingFlexible Nested Orthogonal Antennas,” all of which are entirelyincorporated herein by this reference.

BACKGROUND

1. Field of the Invention

This invention relates generally to electronic systems and methods forlocating buried or otherwise inaccessible pipes and other conduits,cables, conductors and inserted transmitters, and more specifically tosonde and line locators for detecting an electromagnetic signalemissions.

2. Description of the Related Art

There are many situations where is it desirable to locate buriedutilities such as pipes and cables. For example, prior to starting anynew construction that involves excavation, it is important to locateexisting underground utilities such as underground power lines, gaslines, phone lines, fiber optic cable conduits, CATV cables, sprinklercontrol wiring, water pipes, sewer pipes, etc., collectively andindividually referred to hereinafter as “utilities” or “objects.” Asused herein the term “buried” refers not only to objects below thesurface of the ground, but in addition, to objects located inside walls,between floors in multi-story buildings or cast into concrete slabs,etc. If a backhoe or other excavation equipment hits a high voltage lineor a gas line, serious injury and property damage may result. Severingwater mains and sewer lines leads to messy cleanups. The destruction ofpower and data cables can seriously disrupt the comfort and convenienceof residents and cost businesses huge financial losses.

Buried objects can be located by sensing an electromagnetic signalemitted by the same. Some cables such as power lines are alreadyenergized and emit their own long cylindrical electromagnetic field.Location of other conductive lines necessitates their energizing with anoutside electrical source having a frequency typically in a range ofapproximately 50 Hz to 500 kHz. Location of buried long conductors isoften referred to as “line tracing.”

A sonde (also called a transmitter, beacon or duct probe) typicallyincludes a coil of wire wrapped around a ferromagnetic core. The coil isenergized with a standard electrical source at a desired frequency,typically in a range of approximately 50 Hz to 500 kHz. The sonde may beattached to a push cable or line or it may be self-contained so that itcan be flushed through a conduit. A sonde generates a more complexelectromagnetic field than that produced by an energized line. However,a sonde can be localized to a single point. A typical low frequencysonde does not strongly couple to other objects and is thereby unlikelyto produce complex interfering fields that may occur during the tracing.The term “buried objects” as used herein also includes sondes and buriedlocatable markers such as marker balls.

Besides locating buried objects before excavation, it is furtherdesirable to determine the depth of the objects. This is generally doneby measuring the difference in field strength at two locations.

Ground penetrating radar (GPR) may be used to locate non-conductiveobject underground. Using GPR in association with accurate positionalinformation provided by a mapping locating instrument can provideadditional functionality as measurements from multiple known positionsmay be compared and analyzed to form an image of underground structures.

As may be appreciated from the above discussion, both arts are repletewith suggested methods and systems for improving buried object andutility locator operation. In fact, there are several differentfundamental physical approaches to the problems, each of which hasstrengths and weaknesses in different situations. The introduction ofinexpensive processing power and complex software systems has made itpossible for the first time to improve locator performance using agraphical user interface (GUI) to present data obtained from a pluralityof sensors, as disclosed in the above-cited patent applicationsincorporated herein by reference. Portable locators that heretofore havebeen developed offer limited functionality insufficient for quickly andaccurately locating buried utilities. There is still a clearly-felt needin the art for a portable locator system that can operate in any ofseveral different operatorselectable realms, such as the acoustic,electromagnetic and optical realms, to permit effective buried objectlocation under a wide range of circumstances without obliging theoperator to maintain and transport numbers of different systems andapparatus. These unresolved problems and deficiencies are clearly feltin the art and are solved by this invention in the manner describedbelow.

SUMMARY

Many of the above problems are resolved by this invention, whichintroduces a portable locator having at least three support structuresthat allow the portable locator to be selfsupporting and free standing.Each support structure includes a near ground antenna array enclosurethat includes a plurality of antenna elements together capable ofsensing three orthogonal magnetic field components. The self-standinglocator embodiment includes a number of advantageous features andaspects.

The portable locator embodiment also preferably includes anelectro-mechanical accessory mounting interface adapted toelectromechanically accept any of a plurality of various accessories forremovable fixation to the portable locator at or above the groundsurface proximate the supporting structures. According to oneembodiment, a three-axis accelerometer is included. In anotherembodiment, an electronic compass is included.

The attached accessories include a described Ground Penetrating Radar(GPR) device disclosed herein that may include a spinning antenna whoseaxis of spin is approximately vertical, where each transmit pulse can beassociated with a particular angular position of the rotating antenna.In one embodiment, a GPR device is revealed where the round trip traveltime of reflected pulses from any targets away from the spinning antennaaxis varies as a function of rotational position of the spinningantenna. The frequency of the reflected pulses from any targets awayfrom the spinning antenna axis varies as a function of rotationalposition of the spinning antenna due to Doppler shift.

According to another embodiment, the attached accessory is a BuriedElectronic Marker exciter, which transmits a signal to which buriedmarkers may respond, which response is read by the locator to identifythe marker and any information embedded in it. Where reference is madeherein to a dipole transmitter used as a beacon for location mapping,such a transmitter may be a simple dipole coil such as is commonly foundin battery-operated sondes, which emits a dipole field sensible to theappropriately equipped locator at some known frequency such as 512 Hz.When used as a beacon, such a dipole transmitter is typically embeddedin a stand, or in the structure of some device, placed in a fixedposition and used to navigate or measure distances and bearings thereto.Such a beacon serves as a reference point in computing locations,relative coordinates, distances and similar mapping calculations and maybe powered by a battery or other useful means.

According to another embodiment, the attached accessory includeselectrical connections to two or more electrodes that can be placed intothe ground for sensing earth voltages due to electrical cable faults. Inanother aspect, such electrodes may be used for measuring soilconductance between the electrodes and for mapping where the soilconductance over a region can be mapped.

According to another embodiment, the attached accessory includes one ormore acoustic sensors that can be coupled to the ground, and, in oneconfiguration, a separately moveable acoustic transmitter that has anattached magnetic dipole transmitter, the position of which can betracked by the portable mapping locator.

In another embodiment, a method of acoustically mapping a subsurfaceregion is provided, where the mapping locator tracks a dipoletransmitter attached to an acoustic transmitter while employing acousticsensors in a known positional relationship to the acoustic transmitter.

According to another embodiment, the aforementioned method is appliedwhile employing acoustic sensors in a known positional relationship tothe acoustic transmitter; and where a transmitted sound pulse can betimed from modulation of the dipole transmitter signal to establish anacoustic pulse starting time at the portable locator.

In another configuration a transmitted sound pulse can be timed withwireless communication means to establish an acoustic pulse startingtime at the portable locator. Similarly, a transmitted sound pulse canbe timed with one or more microphones on the mapping locator to detectthe air-coupled transmitted sound pulse; such means to establish anacoustic pulse starting time at the portable locator.

According to another embodiment, the attached accessory includes one ormore capacitive sensors that can be coupled to the ground. Becausecapacitance is a function inversely proportional to distance between twocapacitive plates, the accessory enables high resolution distancedetection to near objects underground where precision depth may be ofinterest. In such an application, the object of interest acts as thesecond plate of a capacitive circuit.

According to another embodiment, the attached accessory includes a laserrangefinder to measure the distance to some point in a fixedrelationship to the portable locator or, in another aspect, to measuredistances over a region adjacent to the portable locator.

According to another embodiment, laser target devices may be used incombination with one or more laser rangefinders and one or more locatorsto measure distances directly or indirectly over terrain.

Alternatively, the attached accessory may include a plurality of any ofthe accessory sensor systems herein described.

According to another aspect, a laser range finder can be operatedseparately from the locator and can be identified and mapped by thelocator through means of at least one dipole transmitter, which may bephase-encoded, embedded into the laser range finder or attached toeither side of the laser range finder.

According to another embodiment the laser range finder dipole axis isconcentric with the laser beam axis of the range finder and the dipolecenter is coincident with the point of exit of the laser beam from therange finder.

According to another embodiment, any of the features or functionality ofan attached accessory may be fixedly built into the portable locate andnot be an accessory item.

According to another embodiment, the relative phase of an alternatingmagnetic signal is determined by removing full or fractional (e.g.,one-half) cycles from the transmitted signal in a predetermined manner.

According to another embodiment, the relative phase of an alternatingmagnetic signal is displayed on the screen of a portable locator byshowing motion on the display in one direction or the oppositedirection.

According to another embodiment, the portable locator may be left in afree standing unmoving fixed position, to process signal data for a longperiod of time to narrow the bandpass of the employed digital filters toimprove maximum detection range or signal to noise ratio.

According to another embodiment, the method is disclosed of shifting thecenter frequency of a digital filter away from a near interferingfrequency or harmonic, either measured or based on prediction, to reduceinterference.

According to another embodiment, a locator using some function basedupon the differences between the respective azimuthal and polar anglesof a detected field measured at two locations can modify a displayedline(indicating the buried utility orientation) such as by dithering orblurring the displayed line to indicate hidden utility locationuncertainty due to field distortion causing an imperfect cylindricalfield.

According to another embodiment, a method is disclosed of using themotion of a small hand held dipole transmitter as a means to sketchinformation onto the display screen of the mapping locator.

According to another embodiment, based upon available information, alocator is capable of providing the operator with information posted tothe locator screen if the accuracy of the locate falls within or outsideof acceptable confidence limits.

According to another embodiment, the locator and its accessories arelinked by wireless data links.

According to another embodiment, a display device with independentcomputational capability such as a laptop receives information from oneof more locators or auxiliary devices and is capable of assembling adisplay in layers in which maps of different kinds of detections (forexample, sonic detections, laser ranging, and EMF field measurements)can be geo-coordinated, displayed as separate layers of an integrateddisplay, selectively displayed and otherwise manipulated to enhanceoperator understanding of the relationships between detected objects.

According to another embodiment a sonde or dipole antenna is used incombination with a laser range finder to enable a mapping locator todetect the location of the range finder.

According to another embodiment a separate laser range finder iscombined with a dipole beacon so that a locator can track a positionrelative to a coordinate system of the locator.

The foregoing, together with other objects, features and advantages ofthis invention, can be better appreciated with reference to thefollowing specification, claims and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference is nowmade to the following detailed description of the embodiments asillustrated in the accompanying drawing, in which like referencedesignations represent like features throughout the several views andwherein:

FIG. 1 is a side view of an exemplary self-standing tripod locatorsystem embodiment in an open disposition for operation;

FIG. 2 is a side view of the locator from FIG. 1 in a folded storagedisposition for storage;

FIG. 3 is a top isometric view of the locator from FIG. 1 in an opendisposition for operation;

FIG. 4 is a front detailed exterior view of the accessory mountinginterface;

FIG. 5A is a cross-sectional diagram illustrating an exemplary accessorymounting interface embodiment suitable for use in the locator from FIG.1 with the locator portion of the accessory mounting interface and atypical attachment block shown slightly separated;

FIG. 5B shows the accessory mounting interface of FIG. 5A and theattachment block of a typical accessory joined together as foroperation;

FIG. 6A is a side view of the locator from FIG. 1 in an open dispositionfor operation with the accessory mounting interface coupled to apreferred ground penetrating radar (GPR) accessory embodiment;

FIG. 6B is a top isometric view of the locator from FIG. 6A showing thespinning GPR antenna in more detail;

FIG. 6C is a side view of the locator from FIG. 3 in an open dispositionfor operation with the accessory mounting interface coupled to analternative GPR accessory embodiment;

FIG. 6D is a top isometric view of the locator and attachment in FIG.6C;

FIG. 7 is a bottom view of the locator from FIGS. 6A-B showing thespinning GPR antenna in more detail;

FIG. 8A is a schematic diagram illustrating the locator-target signalpath geometry during operation of the locator from FIG. 6C;

FIGS. 8B and 8C show alternative configurations of the antenna disk inFIG. 7;

FIG. 9A is an illustration of the physical operation of the rotatingdisk antenna used in GPR scanning;

FIG. 9B is a schematic diagram illustrating the relationship between theGPR target distance and GPR antenna rotation for the locator-targetsignal path geometry from FIG. 8A;

FIG. 10A is a schematic bottom view diagram illustrating the GPR signalDoppler shift with an off-axis target for the locator from FIG. 6C;

FIG. 10B is a schematic diagram illustrating the operation of analternative stand-alone GPR apparatus embodiment employing a spinningantenna array;

FIG. 11A is a side view of the locator from FIG. 3 in an opendisposition for operation with the accessory mounting interface coupledto a preferred buried-marker excitation accessory embodiment;

FIG. 11B is a top isometric view of the locator from FIG. 11A;

FIG. 11C is a front view of the locator from FIG. 3 in an opendisposition for operation with the accessory mounting interface coupledto an alternative buried-marker excitation accessory embodiment;

FIG. 12A is a side view of the locator from FIG. 1 in an opendisposition for operation with the accessory mounting interface coupledto a preferred cable fault locating accessory embodiment;

FIG. 12B is a top isometric view of the locator from FIG. 12A;

FIG. 12C is a front view of the locator from FIG. 3 in an opendisposition for operation with the accessory mounting interface coupledto an alternative cable fault locating accessory embodiment;

FIG. 13 is a diagram illustrating a bottom view of the locator from FIG.12A showing the geometry of the cable fault locator accessory and theburied cable fault in more detail;

FIG. 14 is a schematic diagram illustrating a cable fault potentialmapping system suitable for using the locator from FIG. 12C;

FIG. 15 is a schematic diagram illustrating a soil conductance mappingsystem suitable for using the locator from FIG. 14A;

FIG. 16 is a front view of the locator from FIG. 3 in an opendisposition for operation with the accessory mounting interface coupledto an exemplary geophone array accessory embodiment disposed accordingto an acoustic leak detection method embodiment;

FIG. 17A is a schematic diagram illustrating an exemplary acousticmapping system and method of this embodiment employing the locator fromFIG. 16;

FIG. 17B is a side view of the locator from FIG. 1 in an opendisposition for operation with the accessory mounting interface coupledto an alternative geophone array accessory embodiment disposed accordingto an acoustic mapping method embodiment;

FIG. 17C is a schematic diagram illustrating an alternative acousticmapping system and method embodiment employing the locator from FIG. 11Aand other accessories;

FIG. 17D is a top perspective view of the locator from FIG. 1 in an opendisposition for operation and coupled to an alternative geophone arrayaccessory embodiment;

FIGS. 18A-18F are schematic diagrams illustrating a cycle-skippingmethod embodiment for encoding and transmitting relative phaseinformation;

FIG. 19A is a diagram illustrating a graphical user interface (GUI)diagram for indicating relative signal phase to a locator user accordingto an exemplary method embodiment;

FIG. 19B is a diagram illustrating a graphical user interface (GUI)diagram for indicating relative signal phase to a locator user accordingto an alternative method embodiment;

FIGS. 20A-20E are graphical diagrams illustrating a variable band passfilter processing method using a long time period to reduce digitalfilter bandwidth and improve signal-to-noise ratio (SNR);

FIG. 20F is a diagram illustrating a GUI control indicator for theprocessing method for FIGS. 20A-E;

FIGS. 21A-21B are graphical diagrams illustrating an exemplary methodfor shifting a digital filter center frequency away from an interferingpower line harmonic signal to improve locator performance;

FIG. 22A is a diagram illustrating an exemplary locator systemembodiment employing sonde tracing and direct distortion display;

FIG. 22B is a diagram illustrating an exemplary GUI display suitable foruse with the dipole Sketching Method embodiment;

FIG. 23A is a GUI diagram illustrating prior art relating to the 3Dfield-distortion display method embodiment;

FIG. 23B is a GUI diagram illustrating the presentation of the 3Dfield-distortion display method embodiment;

FIG. 23C is a schematic diagram illustrating the distribution of anundistorted magnetic field with respect to the locator from FIG. 3;

FIG. 23D is a view of a two-node locator embodiment equipped withseparate gradient coil antennas suitable for use with thefield-distortion display method embodiment;

FIG. 23E is a schematic diagram illustrating the distribution of adistorted magnetic field with respect to the locator from FIG. 3;

FIGS. 23F-23J are diagrams illustrating a preferred magnetic fielddistortion GUI display embodiment;

FIGS. 23K-L are diagrams of mathematical equations illustratingexemplary features of the magnetic field distortion GUI displayembodiment;

FIG. 24A is a diagram illustrating an exemplary GUI display of adistorted single locate warning for signal properties showing anunacceptable locate result;

FIG. 24B is a diagram illustrating an exemplary GUI display of aslightly distorted single locate warning for signal properties showingan acceptable locate result;

FIG. 25A is a perspective view of an exemplary hand-held laser rangefinding accessory embodiment;

FIG. 25B is a side view of the locator of FIG. 3 in an open dispositionfor operation with the accessory mounting interface coupled to anexemplary hand-held laser range finder embodiment alternatively deployedas an attachment;

FIG. 25C is an overview of an exemplary application of the hand-heldlaser range finder for an example including the locator of FIG. 3 and atarget such as a traffic sign;

FIG. 25D illustrates an alternative laser target embodiment employed inan example using the locator and hand-held laser range finder to measureterrain dimensions;

FIG. 25E is a graphical illustration of a method using two verticallydisposed ball-type laser targets to resolve height measurement. usingthe hand-held laser range finder in FIG. 25A;

FIG. 25F is a graphical bird's eye view of a method to resolve thelocation of a locator in terms of a laser targets coordinate systemusing the locator in FIG. 25B and a laser target;

FIG. 25G is a graphical illustration of a method to use two lasertargets and data from an optional embedded compass to resolve ambiguityin measuring position relative to a baseline;

FIG. 25H is a graphical illustration of a method employing the laserrange device in FIG. 18B and ranging on three laser targets to determinethe position of the locator in a global coordinate system;

FIG. 25I is a graphical illustration of a method using three lasertargets and two locators of the type shown in FIG. 25B to determine therelative locations of the three targets;

FIG. 25 J is an exemplary illustration of a laser target for use inconjunction with the locator in FIG. 25B.

FIG. 25K is an illustration of a side view for the laser target shown inFIG. 25J.

FIG. 25L shows an alternative embodiment of a “lampshade” type lasertarget device equipped with an optional GPS device and an optionaldipole beacon for use with a locator such as that shown in FIG. 25B;

FIG. 25M is a graphical illustration showing the relationship in use ofthe laser target in FIG. 25L and the laser ranging device; and

FIG. 26 is a graphic illustration of one embodiment of a separatedisplay device portraying detection information in user-selectablelayers as described above; and

FIG. 27 is a schematic block diagram illustrating the relationshipsbetween the functional electronic elements of the locator systemembodiment of FIGS. 1-3.

DETAILED DESCRIPTION OF THE EMBODIMENTS The Accessory Mounting Interface(AMI)

FIG. 1 illustrates a side view of an exemplary embodiment of theself-standing tripod locator. According to an embodiment, arrays ofmagnetic sensors responsive to DC magnetic fields and capable of sensingthree orthogonal magnetic field components are included inside one ormore antenna enclosures. According to another embodiment, a three-axisaccelerometer is included, or according to another embodiment, anelectronic compass in included. In one configuration, a compass andaccelerometer on a single integrated circuit such as the AMI-601available from the Aichi Micro Intelligent Corporation, may be embeddedwithin one of the antenna nodes 106, for example. According to oneembodiment, a portable locator includes at least three supportstructures (see FIG. 3) that allow the portable locator to be selfsupporting and free standing. Each support structure includes a nearground antenna array that includes an enclosure with a plurality ofantenna elements (not shown) capable of sensing three orthogonalmagnetic field components. An electro-mechanical accessory mountinginterface is provided to allow various accessory attachments to bemounted to the portable locator at or above the grounds surface near thesupporting structures. In particular, FIG. 1 shows the accessorymounting interface 104 beneath the tripod junction of locatorembodiment. An omnidirectional antenna node (also herein denominatedantenna array) within a casing 106 is located above the accessorymounting interface 104, and similar antenna nodes of which two (108,110) are shown are located at the end of the support structures. In oneembodiment, a DC magnetometer array of at least one axis sensitivity isprovided in one lower node, e.g., 110. In another embodiment, amagnetometer array is situated within each antenna node (106, 108, 110).The magnetometers may include 3-axis DC sensors. In an alternateembodiment, at least one of the magnetometer arrays is combined with a3-axis accelerometer and compass capability such as, for example, isprovided by any suitable complementary-metal-oxide-semiconductor (CMOS)integrated circuit (IC) device, such as the AMI-601 available from theAichi Micro Intelligent Corporation. In this embodiment, the locator isprovided with compass bearing, accelerometer motion and attitude trackinformation, and magnetometric data from the composite device. Such adevice may be mounted centrally, or within one or more of the antennanodes or elsewhere within the structure of the locator. As described inone or more of the commonly-assigned patent references cited above andfully incorporated herein, one or more of the antenna nodes 106, 108,110, 112 preferably includes an electromagnetic (EM) sensor array havingthree substantially-identical EM field sensors each having at least oneconductive coil coupled between two terminals disposed on a flexibleannular wall having a radial centroid defining a sensing axis, and astructure for supporting the three substantially-identical EM fieldsensors such that the corresponding sensing axes are disposed insubstantial mutual orthogonality and the corresponding conductive coilsare disposed in substantial concentricity.

Accessory mounting interface 104 provides a rotationally-indexedphysical mounting point and an electrical interface to physically acceptany of several attachable accessories and to electrically couple theretofor supplying power and exchanging data and control signals. Anaccessory may be simply passive to provide, for example, a variableresistance to the electronic circuits within the locator housing or asophisticated stand-alone system with integral data gathering andprocessing subsystems. When the accessory interface is not in use, aprotective cover is preferably installed. Suitable data interfacesinclude USB 2.0 or IEEE 1394.

FIG. 2 illustrates a side view of the locator 102 from FIG. 1 in afolded storage disposition for storage or transport, showing theaccessory mounting interface 104 and antenna nodes 106, 108, 110.

FIG. 3 illustrates a top isometric view of the locator 102 from FIG. 1,showing the user display 306, keypad 304 and battery compartment 302, aswell as the four antenna nodes (106, 108, 110, 112). As described in oneor more of the commonly-assigned patent references cited above and fullyincorporated herein, the antenna nodes 108, 110 and 112 are eachpreferably disposed at the end of a corresponding foldable supportelement (109, 111 and 113), each of which includes a hinge structureadapted to fold the corresponding support elements 109, 111 and 113 withantenna nodes 108, 110 and 112 against the main locator system support107 for storage (FIG. 2) and to fold the corresponding support elements109, 111 and 113 with antenna nodes 108, 110 and 112 into a level tripodarrangement illustrated in FIGS. 1 and 3, for example.

FIG. 4 illustrates an exterior front view of the accessory mountinginterface 104 showing the upper threaded assembly 512 around the centralshaft 510, a threaded collar 514 covered by an external gripping surface515, a lower collar 516 and a lower shaft section 518 that is acceptedby accessory mounting interface 104 from an attachment (not shown).

FIG. 5A is a detailed section view of the accessory mounting interfaceshowing the locator portion and the attachment portion of the interfaceseparated to illustrate alignment. As can be seen in FIG. 5A, theelectrical connectors 504 of the locator 102 and the electricalconnectors 520 of the accessory attachment are disengaged and theaccessory is partly withdrawn from the locator.

FIG. 5B is a cross-sectional diagram illustrating an exemplaryembodiment of accessory mounting interface 104 showing an accessoryattachment (not shown) fully coupled to the locator accessory mountinginterface. In FIGS. 5A and 5B, the threaded collar 514 couples theaccessory mounting interface 104 to the mating threaded assembly 512affixed to the locator 102. The central shaft 510 is slipped intoreceiving slots in the upper threaded assembly 512 and seated around aconnector assembly 502. Electrical connectors 504 in the locator areembedded into the connector assembly 502 such that contact is made andmaintained with electrical connectors 520 from an inserted accessoryattachment 508 to provide both power and data signal connectivitythereby. The connector unit 520 from the accessory attachment (notshown) is supported by lower collar 516. The accessory mountinginterface 104 provides a tubular receptacle in threaded assembly 512 forthe insertion of accessory attachment 508. A retaining ring 506 retainsthe threaded collar 514 onto the inserted accessory attachment 508.Rotary indexing is provided by a key-and-slot arrangement 522, 524between the receptacle and the inserted accessory attachment. Thekey-and-slot prevents rotation of the accessory once inserted. The lowerthreaded collar 514, when tightened, secures the accessory to themounting interface 104 until released.

The Ground Penetrating Radar (GPR) Accessory

As shown in FIG. 6A, according to another embodiment, the attachedaccessory is a Ground Penetrating Radar (GPR) device 600. Conventionalships' radars use rotating antennas and very narrow beam transmit pulsesto determine bearing to a target. Targets are generally assumed to belying on a plane (ships on the surface of the sea for example) and hencethe specific location of another ship can be determined. Using radar tolocate buried hidden objects is however a very different type of problemand narrow beams cannot be practically formed. Soil penetration depthsfor GPR tend to be shallow, in many areas on the order of a meter or twoin depth. For example, high clay, salty, water saturated soils absorbsradar signals in very short distances. Dry sandy soils may besignificantly more transparent to radar signals. Typical frequenciesused for GPR range from 250 MHZ to 1.6 GHz. Many buried targets ofinterest lie in the first 1-2 meters depth and so operation at veryshort distances is required. As a result, very short transmit pulses areneeded. So-called mono-pulses are used, which are inherently verybroadband. Antennas structures commonly employed produce broad beampatterns and thus very little useful directivity. Essentially, it is notpossible to determine from which direction a reflected target pulse isreceived from a single transmit location without moving the antenna togain the additional data needed to resolve the ambiguity.

The current practice in the locator art is to physically move theantenna across the surface of the ground and to observe thehyperbolic-shaped (assuming a constant antenna translation velocity)target returns to determine the point of closest approach. By repeatedlyscanning (mowing the lawn) in a cross-hatch or raster pattern, an imageor map of underground structures can emerge from sufficient processingand operator interpretation. Until now, GPR surveys requiredconsiderable time and effort to set up and the resulting data was oftendifficult to interpret.

The locator system described and claimed herein solves this problem byfacilitating the determination of the azimuthal direction (compassbearing) to a hidden underground target from data obtained by placingthe locator with accessory GPR device at a single location. Thiscapability allows the operator to move the GPR from location to locationby interacting with the displayed information to rapidly localizetargets of interest.

A key feature of this embodiment is the use of a spinning antennastructure for a ground penetrating radar device (GPR). The antennastructure is rotated around an approximately vertical axis in such amanner that the round trip travel time from any target lying away fromthe axis of rotation varies as some function of the angle of rotation.This variation in range to any target is used to determine the directionto this target. Various antenna geometries are useful, but they allshare the characteristic that the apparent ranges to at least somepossible targets in the volume being surveyed vary with antennarotation. In general it is desirable to offset at least one transmit orreceive antenna element as far as practical from the axis of rotation aspossible to maximize the amount of range variation as the antennastructure completes a revolution.

It is desirable to position a GPR antenna close to the surface of theground to improve coupling of the transmitted signal into the ground.Placing the spinning antenna at a greater distance above the surface ofthe ground, results in a higher fraction of the transmitted energy beingreflected. For this reason it is important that the axis of rotation ofthe spinning antenna structure be approximately normal to the averagesurface of the ground in the area to be surveyed, so that any rotatingantenna element remains positioned as close to the surface of the groundas possible.

This embodiment is directed primarily towards collecting radar datawhile the device in is a fixed location while some antenna elementrotates in such a manner that the bearing and range to an unknown buriedtarget may be determined. The range resolution of the GPR must be lessthan the induced “wobble” in range caused by antenna rotation duringeach antenna revolution in order for the bearing to a target to bedetermined. Methods of calculating detection ranges and bearings fromradar sensors are not discussed herein, as they are wellknown in theart.

Various combinations of antenna geometries can be employed. The simplestis to use a monostatic antenna (transmitter and receiver collocated)where the same antenna is used for both transmit and receive.Alternatively a bistatic antenna can be employed, where the transmittingand receiving antennas are generally not opposite each other from theaxis of rotation. According to another embodiment, the attached GPRaccessory includes a spinning antenna where the axis of spin isapproximately vertical. According to another embodiment, the attachedGPR accessory includes a spinning antenna where each transmit pulse canbe associated with a particular angular position of the rotatingantenna. According to another embodiment, the attachment to theaccessory mounting interface consists of a Shell Casing within whichdifferent devices may be fitted or removed without removing the ShellCasing from the locator.

FIG. 6A illustrates a side view of the locator 102 from FIG. 3 in anopen disposition for operation with the accessory mounting interface 104coupled to a preferred ground penetrating radar (GPR) accessoryembodiment 600 in a position deployed for use. Antenna nodes 106 108,and 110 are also shown.

FIG. 6B illustrates a top isometric view of the locator 102 from FIG. 6Ashowing the spinning GPR antenna attachment 600 with transmitter bow-tieantennas exemplified by one transmit (Tx) antenna shown in twopositions, 608A and 608B, and receiver bow-tie antennas exemplified bythe receive (Rx) antennas 614, 610 and 612, for use in detecting thetarget 606. In FIG. 6B a clockwise-rotating disk 702 carrying a singletransmit antenna (i.e., a bow-tie antenna configuration) sits centrallyin a rigid structure 604 that supports three lobes which, in thisexample, support three non-spinning bow-tie receive antennas 614, 610and 612. It should be noted that the function of the Tx and Rx antennasmay be reversed, or optionally, both Rx and Tx antennas may be switched,for any advantageous combination of receive and transmit antennas thatsuit particular applications. The number of antennas shown is exemplaryonly.

FIG. 6C illustrates a side view of the locator from FIG. 3 in an opendisposition for operation with the accessory mounting interface 104coupled to an alternative GPR accessory embodiment 654, using a shellcasing 656 into which different devices may be fitted. In thisconfiguration, the receive antennas are not mounted on fixed lobes butare included in the spinning segment within the shell, which may be asingle rotating disk, for example, with a monostatic Tx/Rx or otherantenna configuration mounted on it.

An isometric view of the same configuration is shown in FIG. 6D,illustrating the disposition of locator 102, battery case 302, display306, keyboard 304, antenna nodes 106, 108, 110, and 112, the accessorymounting interface 104 and the shell casing attachment 656 with anembodiment of the GPR device 654 fitted to it.

FIG. 7 illustrates a bottom view of a GPR antenna disk and frameassembly 600 where the inner disk 702 is spinning in the ω directionabout a spin axis 708 with transmit bow-tie antenna exemplified by theTx antenna 706 disposed at distance R from spin axis 708, and fixed,non-spinning receive bow-tie antennas exemplified by the Rx antennas610, 612 and 614, disposed at a greater distance from spin axis 708.

One GPR accessory embodiment includes an inner spinning transmit antennawhere the round trip travel time of reflected pulses detected by one ormore receive antennas from any targets away from the spinning antennaaxis vary as a function of rotational position of the spinning antenna.It is readily appreciated by skilled practitioners in the art that whereseveral receive antennas are used, they may receive simultaneously, ormay be switched to receive only in some timed pattern. Additionally thefunction of antennas shown here is an example, and the functions may bereversed, or switched dynamically to best advantage depending on thespecific application. For example, an inner spinning disk with an Rxantenna may be deployed with one or more fixed Tx antennas, transmittingsequentially or simultaneously. Bow-tie antennas are shown herein, butother antenna types may be used. Additionally, multiple antennas atvarious locations may be used, oriented to be more receptive to signalswhich are differently polarized when reflected from targets.

An alternative GPR accessory embodiment includes an inner spinningtransmit antenna where each transmit pulse is associated with aparticular angular position of the rotating antenna and where thelocator is not moving with respect to the ground during data collection.As another example, the attached GPR accessory may include a spinningtransmit antenna where the frequency of the reflected pulses from anytargets away from the spinning antenna axis vary as a function ofrotational position of the spinning antenna due to Doppler shift.

FIG. 8A is a schematic diagram illustrating the locator-target signalpath geometry during operation of the locator from FIG. 6C. In FIG. 8A,the GPR attachment 654 with rotating Tx/Rx assembly antenna 656 locatedinternal to the shell casing detects two radiuses R₁ and R₂ to thetarget object, here a plastic pipe 804, based on detections by thereceiving antenna on rotating Tx/Rx antenna 656, which is at Position P1at time t₁ and at Position P2 at time t₂. The spinning antenna disk isdriven by a motor 806 (not shown) built into the GPR attachment 654 inany useful manner known in the art for spinning a flat disk on a spindlewith an electrical motor.

FIG. 8B is a bottom view of one alternative embodiment of the GPRantenna disk that can be attached within the Shell Casing. In FIG. 8B,two bow-tie antennas 810-812 are shown supported on a clockwise rotatingdisk such that either of the antennas is a Tx antenna and the other isan Rx antenna. In such a configuration, the two (Tx, Rx) antennas810-812 may transmit and receive in timed patterns controlled by aswitching scheme.

FIG. 8C is a bottom view of one alternative embodiment of the GPRantenna disk adapted for attachment within the Shell Casing 654. In FIG.8C, a single monostatic bow-tie antenna 814 is shown supported on aclock-wise rotating disk and configured such that the antenna is a Txantenna when required, and can switch when required to operating as anRx antenna. In such a configuration the antenna may transmit and receivein timed patterns based on a switching scheme.

FIG. 9A shows a bottom view of the inner disk 702 of a GPR antenna thatconstitutes the inner, rotating element of the GPR attachment in FIG. 7.In FIG. 9A, an example of the antenna 706 is shown rotating in {acuteover (ω)} direction from Position 1 to Position 2 through an angle θ.

FIG. 9B is a schematic diagram illustrating the relationship between theGPR target distance and GPR antenna rotation for the locator-targetsignal path geometry from FIGS. 8A and 9A. In FIG. 9B, the two detectedradii R1, R2 from FIG. 9A are shown, and the distances of the antenna608 relative to target 804 (see FIG. 8A) are shown. The values of R1 andR2 define an ellipse such that 2R₁≅R₂.

FIG. 10A is a schematic diagram illustrating the GPR signal Dopplershift with an off-axis target 1004 for the locator 102 from FIG. 6C. InFIG. 10A, a single rotating Tx/Rx antenna 608, at time t₁ receives asignal 1008 while the antenna is moving toward the target 1004. At timet₂ the same antenna 608, now moving away from the target, receivessignal 1010, which when measured at the receive antenna will be lesscompressed by reason of a Doppler shift due to the motion of theantenna. This relative Doppler shift allows target direction to bedetermined.

A stand-alone GPR accessory is described in more detail herein below inconnection with FIG. 10B. A schematic diagram is shown illustrating theoperation of an alternative stand-alone GPR embodiment employing one ormore spinning antennas. In FIG. 10B, the spinning antenna illustrated inFIGS. 6A through 10 is shown built into a moveable cart device 1902. Thespinning Tx antenna disk 1906 rotates around a central axis 1916 in thedirection indicated. A wired or wireless data link 1912 may transmitdata from the GPR unit 1902 to an attached display module 1914 foranalysis by the operator 1904.

A single large bow-tie antenna can be placed either centered on therotating disk or slightly offset from the axis of rotation. Thisrotating antenna configuration can measure a change in signal amplitudefrom a reflected target that varies with antenna rotation as theorientation of the signal pulse polarization relative to an extendedtarget varies as the antenna rotates. Extended targets such as elongatepipes will exhibit varying target strength as a function of the relativeorientation of the polarization of the GPR pulse. A pair of offset,alternately transmitting bow-tie antennas can be employed that areoriented on the rotating disk at right angles to each other. Since manytargets of interest such as pipes have an elongate geometry, a rotatingpolarization can be employed to advantage to provide an indication ofthe direction of target elongation.

The Buried Electronic Marker Accessory

FIG. 11A shows another embodiment, wherein the attached accessory is aBuried Electronic Marker exciter that transmits a signal to which buriedmarkers can respond. FIG. 11A is a side view of the locator 102 fromFIG. 1 in an open disposition for operation with the accessory mountinginterface 104 coupled to a preferred buried-marker excitation accessoryembodiment including the Marker Excitation attachment 1104 and anembodiment of the Shell Casing 1102. The mapping array locator 102 incombination with an EM activator offers many unexpected advantages forlocating a buried marker and displaying location indicators to the user.When a buried marker is excited by a pulse of energy from the accessory1104, it resonates by design to the frequency of the energy transmitted.The pattern of such resonance identifies the marker when it is detectedby a receive coil in the Buried Electronic Marker accessory or,alternatively, by the lower antenna nodes 108, 110, and 112 (notvisible) of the locator 102.

This resonance may be used to carry an encoded response based oninformation previously encoded into a marker such as its identification,type, date of installation, or similar data. The response resonance isdetected and parsed by the locator 102 through the lower antenna nodes108, 110 and 112 (not shown here) or by the receiver coil of anaccessory attachment when so equipped.

FIG. 11B is a top isometric view of the locator 102 from FIG. 11Ashowing three lower antenna nodes 108, 110, and 112, and the shellcasing 1102 and Buried Electronic Marker attachment 1104 attached bymeans of the accessory mounting interface 104.

FIG. 11C illustrates a front view of the locator 102 from FIG. 3 in anopen disposition for operation with the accessory mounting interfacecoupled to the Buried Electronic Marker accessory embodiment 1104,connected by means of the shell casing 1102. In FIG. 11C, a buriedmarker 1106 is excited by an energy pulse emitted from excitation coil1108 within the accessory 1104, and resonates in response at apredefined frequency that is detected by locator 102 by means of lowerantenna nodes 108, 110, and 112, or optionally by means of a suitablereceiving circuit (not shown) in the attachment 1104. The responsedetection is then parsed into marker information that may be displayedby the locator 102. An alternative means of display using an externaldisplay device such as a laptop computer may also be used and isdiscussed below with FIG. 26.

Note that for many accessory or peripheral devices, such as the BuriedElectronic Marker attachment, an accessory may be adapted to use with alocator not equipped with an accessory mounting interface when suchaccessory is configured with its own power and electronics, such as bybeing clipped to a locator mast or deployed separately from the locator.

The Cable Fault Locating and Conductance Measuring Accessory

Turning to FIG. 12A, according to another embodiment, the attachedaccessory is a fault detector 1202 that includes electrical connectionsto two or more electrodes that can be placed into the ground for sensingearth voltages such as those due to electrical cable faults. Theseelectrodes or probes can be used for sensing earth voltages where theelectric field potentials can be measured and mapped. FIG. 12A is a sideview of the locator from FIG. 3 in an open disposition for operationwith the accessory mounting interface 104 coupled to a preferred cablefault locating accessory embodiment 1202. In FIG. 12A, the faultlocating accessory 1202 is attached by means of the accessory mountinginterface 104 and consists of a frame 1222 that supports multipleprobes, of which three 1212, 1206, 1208 are here shown.

FIG. 12B is a top isometric view of the locator 102 from FIG. 12A. Theattachment 1202 is coupled to the locator 102 by the accessory mountinginterface 104 and consists of a frame 1222 supporting four separateprobes of which probe 1206 is central and probes 1212, 1208, and 1210are disposed to align between the axes of the three lower antenna nodes108, 110, and 112. The probes 1206-1212 and their support frame 1222 aredesigned to facilitate insertion fully into the ground to measureinter-probe electrical potentials. The frame provides depressions on thetop surface above each probe to support operator foot pressure appliedto sink the probes into the ground. The probes are individually fittedwith hinges 1218, 1220, and 1222 so that they may be either folded up orlocked in an open disposition for use. As may be readily appreciated bythose skilled in the art, this use of multiple probes in fault locationimproves the traditional art in which A-frame devices with two probesare used with one-dimensional informational results. In an alternativeembodiment, the probes may be extended on flexible conductors forplacement away from the locator.

FIG. 12C is a front view of the locator 102 from FIG. 12B in an opendisposition for operation with the accessory mounting interface 104coupled to an alternative cable fault locating accessory embodiment1202. FIG. 12C illustrates probes 1212, 1210, 1208, and 1206 insertedinto the ground for the purpose of determining the location of a fault1240 in a buried cable 1238 by a method discussed below in connectionwith FIG. 13.

FIG. 13 is a diagram illustrating a bottom view of the locator from FIG.12A showing the geometry of the cable fault locator accessory with afirst electrode 1208, a second electrode 1210, a third electrode 1212and a fourth central electrode 1206. To determine the location of fault1302, the locator system employs an embedded program element (FIG. 27)to analyze electrical potential among all four probe locations andproduces the following voltage difference array:

$\quad\begin{bmatrix}{V_{1} - V_{2}} \\{V_{1} - V_{3}} \\{V_{1} - V_{4}} \\{V_{2} - V_{3}} \\{V_{2} - V_{4}} \\{V_{3} - V_{4}}\end{bmatrix}$

The resultant voltage difference array is used by the program element todevelop the Graphical User Interface (GUI) indicators adapted to directthe operator to the fault. By referencing the voltage gradients detectedin comparing V₁, V₂, and V₃ with the central probe, V₄, an additionalobservation is obtained.

FIG. 14 is a schematic diagram illustrating a cable fault detectionmapping system suitable for using the locator 102 from FIG. 12C. In FIG.14, a cable fault attachment comprising one or more electrodes coupledby means of the Attachment Mounting Interface 104 in locator 102 is seenusing a remote ground probe 1404 to which it is attached by a clamp 1402and a coil cord 1414 from the locator 102. Further in FIG. 14, a dipolenavigational beacon 1406 is deployed at a distance from locator 102. Thebeacon 1406 emits a dipole field 1408 detectable by the antenna arrays108-112 of locator 102. In FIG. 14, the locator system 102 is used toisolate the location of fault 1410 by mapping the gradients of thecomposite field 1412, which are in part shaped by the dynamics of theelectrical fault to ground 1410 caused, for example, by abradedinsulation in the target cable. Comparing multiple measurements ofelectrical potential and combining their information with the measuredlocation of the beacon 1406 can provide a solution for the location offault 1410. As may be appreciated by those skilled in the art, themethod described may be conducted with as few as one single electrodeand a remote connected ground probe, or with any combination of multipleelectrodes found to be advantageous in application. The user display, insuch an implementation, guides the user to the point of maximumpotential, which places him directly over fault 1410 in this scenario.

FIG. 15 is a schematic diagram illustrating a soil conductance mappingsystem suitable for using the locator from FIG. 14. In FIG. 15 locator102 is used to determine voltage gradients as described above inmultiple locations (labeled as a, b, c, and d in FIG. 15) for use inconstructing a voltage map of an area. The soil conductance variabilitycaused by moisture from a water leak 1514 in a buried pipe 1512influences the resultant soil conductivity map, which can lead tolocating leak 1514. In doing so, the locator measures and stores inmemory the electrical potential readings from each of the four probes ateach of the four points 1 a, 2 a, 3 a, 4 a, for example. In FIG. 15, apositional reference beacon 1504 that emits a dipole field detectableand measurable by locator 102 provides positional information to thelocator. A second positional reference beacon 1506 is equipped with asimilar dipole emitter as well as a GPS receiver. The beacon 1506 emitsa dipole field that can be sensed and measured by locator 102. A datalink using Bluetooth or Zigbee or similar wireless protocols may beintegrated into any of the several devices used in conjunction with thelocator 102; here, such a link connects beacon 1506 with locator 102 andprovides world-coordinate location data to it. Note that remote beaconssuch as those used here may be located relative to locator 102 by theuse of dipole field detection or by wireless transmission of GPS datawhere such a beacon is so equipped. The background lines representiso-voltaic lines in a voltage gradient map. It may be appreciated bythose skilled in the art that a method of using one or more probes and acommon ground stake attached by means of a coil cord, for example, asshown in FIG. 14, is useful in the mapping scenario shown in FIG. 15,and that fewer probes may otherwise be employed, as found to beadvantageous in a specific application. In conductance mappingapplications, a voltage may be injected at one probe and measurement ofthe potential or current taken at another probe. Such a high-impedancemeasuring system is useful for measuring soil conductivity in terms ofvoltage or current, or both

The Leak Detection Accessory

According to another embodiment, the attached accessory sensor systemmay be embodied as one or more acoustic sensors adapted for coupling tothe ground. Such sensors facilitate use of the locator system inlocating physical leaks from pipes carrying fluids such as water bysensing and analyzing relative strengths and patterns of sound signals.FIG. 16 is a front view of the locator 102 from FIG. 3 in an opendisposition for operation with the accessory mounting interface 104coupled to an exemplary geophone array accessory embodiment 1622disposed for use according to an acoustic leak detection methodembodiment. In FIG. 16, locator 102 is coupled through its accessorymounting interface 104 with an array 1628 containing three geophones1610, 1612, and 1624 triangularly disposed in a rigid frame such thatthe sensor ends of the geophones are placed into or on the ground. In analternative embodiment, the geophones may be extended on coil cordsexemplified by the coil cord 1626, and deployed some distance away fromthe locator 102. Dipole location beacons (not shown) may be included ingeophones to provide accurate positional location relative to locator102. Dipoles may be continuous or intermittent in operation. A separatefree-standing geophone 1620 is also shown inserted into the ground at adistance from the locator 102 and equipped with a battery unit 1602 andwith a two-way wireless link 1608 by means of which detections made bygeophone 1620 and their times of detection are transmitted along a path1606 in real time to a wireless link 1604 in the locator 102. Further inFIG. 16, a buried pipe 1618 with a leak 1616 at an unknown location isshown, from which escape sound waves 1614 caused by the turbulentpassage of liquid through the leak. The sound waves are detected bygeophone sensors 1610, 1612, 1620 and 1624 at different times, as afunction of the speed of sound through the particular soil being probed.By correlating sound wave detections digitally, the locator 102 maydetermine the bearing and distance to the source of sound waves 1614 andthereby determine a probable location of the leak 1616, using any usefulmethods known to the art for correlation and cross-correlation ofsignals.

The Acoustic Imaging and Mapping Accessory

Attention is now directed to FIG. 17A. According to another embodiment,the attached accessory includes one or more acoustic sensors that can becoupled to the ground and a separately moveable acoustic transmitterthat has an attached magnetic dipole transmitter, the position of whichcan be tracked by the portable mapping locator.

A method of acoustically mapping a subsurface region is introduced fortracking a dipole transmitter attached to an acoustic transmitter whileemploying acoustic sensors in a known positional relationship to theacoustic transmitter, where a transmitted sound pulse can be timed(e.g., by means of wireless communications) to establish an acousticpulse starting time at the portable locator. Alternatively, thetransmitted sound pulse may be timed with one or more microphones on themapping locator to detect the air-coupled transmitted sound pulse.

According to another embodiment, the attached accessory includes one ormore acoustic transmitters that can be coupled to the ground. Accordingto yet another embodiment, the attached accessory includes one or moreacoustic sensors and one or more acoustic transmitters that can becoupled to the ground. According to another embodiment, the severaltransmitters and sensors not directly connected to the mapping locatormay be linked to it through a wireless data link such as by Bluetooth,Zigbee or other wireless protocol.

FIG. 17A is a schematic diagram illustrating an exemplary acousticmapping system embodiment and method employing the locator 102 from FIG.16. In FIG. 17A, a mapping locator 102 is equipped with at least onemicrophone 1704 and is shown with the geophone array accessory 1622coupled to the locator 102 through the accessory mounting interface 104.FIG. 17B shows the scenario from FIG. 17A, with an alternative geophoneembodiment 1624 disposed remotely from the locator 102 and connected bymeans of a coil cord 1626. In FIG. 17A, a sound-generating deviceembodiment capable of injecting significant sound energy into the groundis shown to include a steel column 1702 struck by a heavy hammer 1718.Any other useful device may be used, such as a sonic boomer or acartridge-firing nail gun, for example, or any other device or methodfor injecting sufficient sonic energy into the ground at a known moment.In FIG. 17A, the sound generating device is equipped with a dipoletransmitting beacon 1716 that can be detected and whose location can bemeasured by the locator 102, and is further optionally equipped with awireless link capable of transmitting a timing signal 1722 to thelocator when the column in this example is struck. As illustrated, thestrong sound energy 1714 emitted from the column when struck travelsthrough the soil and is reflected from a buried pipe 1712. The reflectedsound energy 1710 is detected by the geophone array 1622. The locatoralso detects the original sound waves 1726 from the striker 1718 hittingthe column 1702, by means of at least one built in microphone 1704. Boththe primary sound impulse 1714 and the reflected sound 1710 are detectedat slightly different instants in time by the several geophone sensors1610, 1612, and1624, which are components of the accessory sensor array1622. Note that where geophone element 1624 is disposed remotely fromthe locator 102 on a coil cord 1626, some means is required fordetermining the exact distance from locator 102 to geophone 1624, suchas a small dipole embedded into the geophone and detectable by thelocator 102, or a useful mechanical means for measuring or defining thedistance, for example. Each of the sound signals arriving at the locatoris time-tagged digitally, and the comparison of the timing of thesevarious signals with the optional radio-link timing signal 1722 and theknown location of the dipole transmitter 1716 enables the mappinglocator to determine the relative distance of the buried pipe 1712 frommore than one point, thereby facilitating computation of its bearing.Any useful correlation and cross-correlation techniques may be used inprocessing the signal data for direct and reflected sound impulses.

FIG. 17C illustrates an acoustic mapping system and method. An optionalexternal geophone 1620 is equipped with a dipole coil, an externalbattery 1602 and an antenna 1608 for exchanging signals and databidirectionally along line-of-sight 1752 with locator 102. A mappinglocator 102 is shown with an alternate embodiment of the geophone sensorcoupled to it by means of the accessory mounting interface, in this casea flat-surface geophone 1702 suitable for use on a flat hard surfacesuch as a floor or concrete slab, for example. An optional separategeophone 1734 with its own dipole coil 1736 is shown connected to thelocator by an optional wire connector 1737. Also connected to thelocator 102 by a separate wired connector 1739 is an optional acousticsource 1754 that may also contain a battery power supply (not shown) toextend operation time. Further in FIG. 17C, the underground area isshown to be populated with a buried three-line conduit 1750 thatemanates electromagnetic flux 1748 by reason of electric current beingcarried in one or more of its conductors, such flux being detectable bythe locator 102; a water-pipe 1746 that has a leak 1744; and by a sewerline 1742 into which has been placed a pipe-inspection camera 1740 on apush cable (not shown), equipped with its own dipole sonde. The locator102 is disposed on a concrete slab 1738 and operates to simultaneouslydetect and report the locations of each of the targets illustrated.Sound pulses emitted by the acoustic source 1754 are detected by theseveral geophones 1608, 1702, and 1736 at different times depending onthe transmitting media, and are reflected from objects 1740, 1746, and1750, which reflections are similarly detected at varying delay timeswith respect to the corresponding impulses from source 1754. Whencombined with timing signals provided by the acoustic source 1754 andthe time-tagged detection information relayed by the several geophones,this provides sufficient information to locator system 102 to facilitatethe computation of an acoustic map of the reflecting objects.

FIG. 17D is a top perspective view of the locator 102 in an opendisposition for operation and coupled by a wired connector to anacoustic receiving array 1782. In such a configuration, the accessorymounting interface 104 may be left unoccupied. Alternatively, as shownhere, the acoustic array accessory 1782 may be equipped with a cable1790 terminating in a plug 1794 adapted to couple to the accessorymounting interface 104, thereby facilitating transfer of power and datathrough the AIM 104. The acoustic receiving array embodiment 1782includes two embedded dipoles 1784 and 1786, each distinguishable by thefrequency or the modulation of the respective emitted EM field, aredisposed within two opposing corners of the array 1782, therebyproviding means for the locator system 102 to detect the relativelocation of array 1782. The array 1782 includes a multiplicity ofacoustic sensors and locator 102 incorporates means for distinguishingand integrating acoustic sensor signal information into an acoustic map,either through embedded processing and program elements (not shown)within the array 1782 or by program element means (FIG. 27) in thelocator system 102.

Many useful methods for the acoustic location of buried utilities andutility faults are known in the art. Electrical faults in cables can bemade to produce sound by repetitively energizing the cable with a largecapacitor. Each discharge of the cable produces a “thump” at the site ofthe fault. Simple mechanical and electronically amplified stethoscopescan be used to iteratively search for fluid leaks in pipes and thethumps produced in faulted cables. Proper usage of such devicespresupposes a knowledge of the location of the pipe; see, for example,“Instructions for using Globe Geophone” by Heath Consultants. Digitalsignal processing can be applied to the signals from several geophonesto beam form. The inclusion of geophone beam forming and/or crosscorrelation in a portable locator enables several new techniques. Theportable locator can often locate both the leaking utility and nearbyburied utilities by stray electromagnetic emissions from the utilitiesand show on a portable display the location of the leak relative tonearby utilities.

The portable locator system embodiment with an acoustic detectionaccessory can be used to insure that the acoustic detectors are placedadvantageously with respect to the buried utility. Many soils arestrongly attenuating for sound. Acoustic sensors that are misplaced evena few meters may not receive any usable acoustic signal. The acousticdetector accessories may include low frequency magnetic dipole sourcesthat can be tracked by the portable electromagnetic locator. Theacoustic processing scheme embedded into the portable locator thus hasaccess to both the relative position and orientation of the acousticsensors. Relative orientation is particularly important in the casewhere the acoustic sensors are three-axis sensors. The acoustic signalfrom interfering noise sources often propagates as a ground wave withsubstantial horizontal components, where the leak signal or thumpersignal are generally nearly vertical. Usually the horizontal componentsof the acoustic signal arrive from a different azimuth than theinterfering signals. Knowledge of the relative orientations of sensorsand utilities can be used to facilitate the construction and training ofadaptive noise canceling filters, adaptive beam formers, andmatched-field processing.

A variety of sound sources may be included as accessories for theportable locator system 102. Impulsive hammers may be manually actuatedor pneumatically, electrically, or hydraulically actuated. When trackinga horizontal drill, for example, the acoustic source can be driven byenergy from the available pressurized drilling mud. The horizontal drillacoustic source may be specifically designed as an acoustic source orthe noise may be produced by a rock drill hammer attached to the string,for example. Often the noise produced by the interaction of the drillhead with rocks and cobble produces sufficient acoustic energy to permitacoustic tracking of the drill string and acoustic imaging of nearbyutilities, for example.

Some parameters of pipes may be derived from the acoustic energyscattered by the pipes. The lowest frequencies modes of pipes arebreathing modes. In the breathing modes, the prime contours of thecylindrical shell move in and out. At mid-frequencies, anti-symmetricand symmetric leaky Lamb waves are strong contributors to thescattering. The high frequency scattering is controlled by the wallthickness of the scattering pipe or conduit.

An acoustic sensor can be embodied as, for example, electromagneticmoving coil, moving magnet, piezoelectric, or a combination thereof forgreater bandwidth. Piezoelectric sensors have the advantage of lesscoupling from the navigation sondes to the acoustic sensor. In mostapplications, the sonde can be turned off after 10 to 20 seconds ofposition integration, so electromagnetic inference is not a problem. Arecurring problem in leak detection and seismic imaging is wind noisecoupling into the acoustic sensors or geophones. The locator system mayinclude several other microphones that are reasonably decoupled fromground motion and suitable for use in adaptive noise cancellation.Multiple microphones each with a cardioid or other directional beampattern may be used to facilitate cancellation of several differentnoise sources, for example. Suitable geophones include bothunidirectional phones and multidirectional phones responding to soundfrom multiple axes. Geophones in this embodiment may be either uni- ormulti-directional.

Because dry soils are poor transmitters of acoustic energy, theytransmit GPR energy well; conversely, moist soils defeat GPR bydissipating the energy injected from a GPR Tx device rapidly, whilemoist soils lend themselves to good results in acoustic scanning. Anadditional advantage of acoustic tomography is that it identifiesplastic pipes that cannot be traced by normal locating techniques in theabsence of a tracing wire. The acoustic array 1782 described herein, orthe geophone array 1622 shown in FIG. 16, may also be employed in amethod known as “acoustic day lighting,” under suitable conditions. Inthis approach, the ambient sound caused by, for example, passing trucks,railroad trains, or cars in an urban environment, provides enoughambient energy to enable detection of buried objects by passive receiptof reflected sounds.

Both the microphones and the acoustic sensors can include low-noisepreamplifiers before capturing the signal at 24-bit analog-to-digitalconverters (ADCs) such as the Texas Instruments ADS1252. The signals maybe processed in a fixed-point processor such as the TMS320VC5441, whichhas the 12 MB/S ports capable of interfacing with ADCs such as theADS1252.

The Cycle-Skipping Phase-Encoding Method

FIGS. 18A-18F are schematic diagrams and charts illustrating anembodiment of the cycle-skipping method for encoding and transmittingrelative phase information. The preferred method is to periodicallyphase-flip an alternating-current (AC) drive waveform by droppinghalf-cycles at predetermined intervals. The drive waveform may be asquare-wave output that is direct connected to the target utility, or itmay be an induced sinusoidal waveform. An induced waveform is preferablycreated in a high-Q LC-tank circuit adapted for suspending the tankoscillation by switching the capacitor (C) out of the tank circuit (byopen-circuiting C) at maximum capacitor voltage or, alternatively, byswitching the coil (L) out of the tank circuit (by short-circuiting L)at maximum coil current. This display method is modulated by andcooperates with the defocused line display method described hereinbelow.

The method of cycle-skipping is used to interpret phase, and thereforecurrent direction, and can be used with direct-connect locating toindicate the direction of current flow with respect to the locatorsystem position. The technique may also be designed into trans-mittersby suspending resonant high-Q tank resonators in an inductivetransmitter, as described. In an alternative embodiment, a skippedfractional-cycle transmission will permit information transmission froma sonde, from a drill head used in HDD applications, or from a buried EMmarker, for example. The cycle-skipping method may skip entire cycles,which advantageously maintains signal phase, or may skip fractionalcycles (e.g., half-cycles), which provides easier detection by locatorsystem 102. A predetermined skipping pattern may be selected for thetemporal asymmetry necessary to facilitate phase identification.Half-cycle skipping can be implemented as a phase lock loop (PLL)circuit.

FIGS. 18A through 18F are a disclosure of an exemplary mathematicalmethod by which a cycle-skipping technique can be used to calculatephase and current direction. Other approaches may be used. FIG. 18Ashows a plot of an unmodulated waveform against a unit circle, with realvalues plotted on the x axis and imaginary numbers on the y axis. Anexample of the unmodulated waveform as received from an antenna node isillustrated in FIG. 18B. FIG. 18C describes a series of Mathematicafunctions for producing half-cycle modulation patterns, which producethe positive, negative or zero values shown in FIG. 18D when applied.These modulation values are used as inputs to modulate a localoscillator, with output results shown in FIG. 18E. A cross-correlationof input signal and reference signal is then performed using thefunctions described in FIG. 18F, with the resultant values shown. Thesepost-filtering values are positive for a current in one direction, suchas away from the transmitter, and negative for a current direction inthe opposite direction, such as approaching the transmitter. The phasevalues are greater than zero in FIG. 18F. The positive or negative signof the signals in FIG. 18F are available in locator system 102 for usein providing a phase-encoded graphical user interface (GUI) diagram ondisplay 306 (FIG. 3), for example, as is now described.

The Phase Encoding Display Method

FIG. 19A a graphical user interface (GUI) diagram illustrates anexemplary embodiment of a method for indicating relative signal phase toa locator user. In FIG. 19A, the display mapping area 2102 of thelocator is shown displaying a detected line with moving dots shown oneither side of it. The dots on the sides of the trace line are displayedas moving in lock-step, either toward the top of the display or towardthe bottom, depending on the display indicator representing the detectedcurrent direction. The current direction is calculated from the phasedirection determined by the fractional cycle-skipping phase-encodingmethod discussed above.

The visual indicator display shows current direction, which is directlycorrelated to phase, along a linear display feature representing thedetected line, by using the apparent motion of objects in the displaymoving along the direction of the linear feature. This is referred to bysome as a “marquee” type of display and by others as a “crawling line”display. Current direction may also be represented by drifting clouds,chevrons, arrows, or particles, for example. The specific visualindicator may be embodied as any useful image for conveying a sense ofmotion along a linear object displayed as representative of the detectedutility line, pipe or cable. Another preferred embodiment is shown inFIG. 19B, in which the visual indicator used is a series of arc-segmentswithin a channel aligned to represent the detected utility line andindicating current direction by the direction of their curve. A simplearrow may also be employed.

The Variable Time-Bandwidth Locator System Processing Method

FIG. 20A illustrates another locator embodiment that is equipped withvariable time-bandwidth filtering circuits for significantly improvingthe displayed signal when provided with data samples sufficient toidentify noise elements.

FIGS. 20B-E are graphical diagrams illustrating a variable bandpassfilter processing method performed by one or more program elements (FIG.27) in the locator processor 2202 (FIG. 20A) that uses a longaccumulation time to improve signal-to-noise ratio (SNR). FIG. 20B is achart showing an exemplary signal waveform 2204 captured by a locatorsystem 102 that is processing antenna node (106-112) detectionsintegrated over a time-window of 200 milliseconds, with the locatorsystem passband centered on 8192 Hz as a frequency of interest. Asshown, the signal at the frequency of interest in FIG. 20A is buried inambient noise and cannot be visually distinguished. FIG. 20C depicts thesame signal as it may appear when the locator continues to receive andprocess signal samples at the location used in for signal 2204 in FIG.20A for an integration period of 1 second. FIG. 20D depicts the samesignal as it may appear when the locator remains stationary andcontinues receives and processes signal samples for a period of tenseconds, with a corresponding increase in SNR. FIG. 20E depicts the samesignal displayed after an integration period of 100 seconds.

FIG. 20F is a diagram illustrating a GUI control indicator for thevariable bandpass filter processing method illustrated in FIGS. 20B-E.In FIG. 20F, the locator GUI display screen includes visual indicationof the sample window in use by the variable pass bandwidth control 2204.In the example, the variable pass bandwidth is set to analyze a sampleof 2 Hz. The filter can be set for larger band-widths, such as 8 Hz, orsmaller band-widths such as ½ Hz or ¼ Hz. When the filter is set low,such as ¼ Hz, more samples are collected, requiring a longer period toprocess a block of data but producing a higher SNR. Conversely, when thefilter is set to a higher value, such as 8 Hz, the SNR is lower, but theresponse time of the locator to changing conditions is proportionatelyfaster, as fewer samples are being processed. This innovation isadaptable for use during portable locating and improves the informationmade available to an operator, whether or not the locator isself-standing. The adjustment of the variable pass bandwidth settings asa function of signal clarity can be automated in a program elementwithin the locator processor (FIG. 27).

Two primary modes are used in applying the filtering. In narrow-bandfiltering, directly-applied digital filters can respond rapidly, buttend to lose precision over a sampling time exceeding around fiveseconds. Broadband filtering, by contrast, uses correlating andcross-correlating methods to build an additive picture over longerperiods of time, which improves in accuracy as the process continues.

The Known Power-Line Harmonic Frequency Avoidance Method

FIGS. 21A-21B are graphical diagrams illustrating an exemplary methodfor shifting a digital filter center frequency away from power lineharmonics to improve locator performance. This method was successfullytested by the inventors and has proven useful. In FIG. 21A, a graphicillustration depicts a non-shifted frequency map in which the 1024 Hzband being sought with a portable locator is compromised because ofsignal leakage from a lower band, here 1020 Hz, the 17^(th) harmonic ofubiquitous 60 Hz power. The method presented consists of imposing ashift to the right by an increment, in this example, of 3 Hz, thuscentering the same symmetrical signal curve around a value of 1027 Hz.This shift provides a clearer signal at 1024 Hz because the signal curveis now outside the influence of the harmonic noise at 1020 Hz. With thenoise element shifted out of band, a lower but clearer signal of thetarget frequency (1024 Hz) is obtained. In both FIGS. 21A-B,signal-to-noise is defined by the ratio B/A, which by inspection of thediagrams is clearly enhanced in FIG. 21B over FIG. 21A.

The Display Sketch Method

Looking to FIG. 22A, another embodiment is shown wherein an operator isprovided with a specialized dipole sonde configured as a stylus withwhich hand-drawn markups or annotations may be made on a GUI displayscreen and then stored, recovered, or transmitted for further use. FIG.22A is a diagram illustrating an exemplary locator embodiment employingdipole-enabled sketching on the locator's display. In FIG. 22A, theoperator holds a batterypowered dipole sonde 2402 configured so as tofit to the average hand, and by moving it across the display screen 306the operator can annotate the display screen as it is shown at any pointin time. An example of the result of such annotation is shown in FIG.22B, where the operator, using the sonde as a stylus, has annotated thedisplay screen 2508 with a note 2802 that the display is showing thetrace of a gas line. Annotated screens can, for example, be printed outwith a “locate ticket” through software in an independent laptop ornotepad screen device, or simply preserved at the locator for notetaking or diagramming use later. In this aspect, a small sonde is fittedwith a push-button switch, which, when activated, causes movement of thesonde to act as a stylus drawing a line as the sonde is moved when theswitch is activated and the sonde is over the GUI screen. The switch maybe pressure activated from the contact point with the screen, oractivated manually by the operator. The drawing routine stops when theswitch is deactivated such as by the sonde being lifted from the screenor manually switched off.

Various means can be used to associate the operator controlled movementof the sonde used for display sketching. The upper antenna node 106 candisplay a sonde pole, where the field lines are near vertical. Theoperator can move the image of the pole on the screen by manipulation ofeither tilt or the position of the sonde. Alternatively, the fullantenna array can be used to position the sonde and space and the truespatial movement of the sketching sonde can be used to drive the tracingcursor on the display screen.

The “3D” Direct Distortion Display Method

Turning now to FIGS. 23A and 23B, another embodiment is shown wherein avisual indication of a detected trace line on a locator GUI display isenhanced with clouding, blurring, or other suitable modulation toreflect the lack of clarity or “distortion” in the local EM field atlocator system EM detectors and processed mathematically by thelocator's processor.

In line tracing, distortion typically represents the deviation of themeasured field from an expected cylindrical geometry. The “quality” ofthe EM field radiated from a buried utility is useful operatorinformation because it determines how accurately the locating device canestimate depth and position of the utility. Poor quality EM fields aredefined herein as weak, noisy, or heavily-distorted fields. Weak andnoisy fields often result from poor conduction of the energizing signalon the buried utility or improper hookup of the transmitting device.Distortion can be caused by a number of factors, including coupling ofthe field onto nearby conductors, large ferrous objects such as cars orutility boxes in the near vicinity, weak conduction on the buriedutility, and jamming signals.

FIG. 23A is a GUI diagram illustrating the presentation of the 3Dfield-distortion display method in prior art using two separate displaylines 2506, 2504 to indicate the trace as detected by the upper andlower antenna arrays of a two-node locator. An example of such a locatoris illustrated in FIG. 23D, which shows the three axes of B-fielddetection for the upper node 2354 and lower node 2356, on which thecalculation of distortion is based. Increasing distortion is indicatedby an increasing difference in alignment and orientation of the top andbottom node 3D B-field measurements.

FIG. 23B is a GUI diagram illustrating the presentation of a directfield-distortion display method embodiment. FIGS. 23A and 23B show thatthe distortion of a field is calculated from both the azimuthal andpolar angles of the trace lines. The polar angles govern the trace lineseparation from the center of the display field, while the azimuthalangle governs the trace line bearing. In FIGS. 23A and 23B, the lowerNode Signal line 2506 (from node 2356 in FIG. 23D) and the blurredsignal line 2510 are in the same place. The method for the calculationand display of a composite distortion signal in this manner is equallyapplicable, for example, to a two-node or a multi-node locator, such asthe example locators shown in 23C as locator 102 and in 23D as locator2352.

FIG. 23C is a schematic diagram illustrating the distribution of anundistorted magnetic field with respect to the locator from FIG. 3. Thestrength of the field in an ideal circular field varies inversely withR, where R is the radius 2602 from the conductor's center to the pointof measurement.

FIG. 23E is a front view illustrating the distribution of a distortedmagnetic field with respect to the locator from FIG. 3. Because thefield is a composite caused by multiple conductors 2710, 2714, and 2716,the measurement of field strength is not be directly and consistentlyinversely proportional to the value of R.

Returning now to FIG. 23B, a linear feature 2510 is shown on the mappingarea 2508 of the display of a locating device, and the visual indicatoris enhanced by blurring the line or softening or defocusing ordisturbing in a way that visually indicates positional uncertainty inthe detected object and thereby communicated to the operator of theportable locating device with simple inspection of the visual featuresof the image representing the object on the display. The width of theblurring 2512 is made proportional to a measure of the degree ofdetected distortion. Clouding the display line in this fashionproportionate to distortion is merely one of many useful indicators fordistortion, any of which need merely project a suitable degree ofuncertainty to the user. For example, other such indication means mayuse colors, fading displays, different symbols or various any othersimilarly useful visual and aural user interface mechanisms known in theart.

The method illustrated uses spatially separated full field data, wherethe relative positions of the measurements with respect to each otherare known, to calculate the depth and position of a buried conductor. Itis highly advantageous to have the field sensors as close to the targetas possible. There are two important embodiments. The first emphasis isto fit the data to a cylindrical field model to create more accuratepositional information, as well as to calculate a quality figure ofmerit that would usually be recorded for Geographical Information System(GIS) purposes. Such purposes may include, for example, the developmentof a geographically-coordinated database of past locate results. Theself-standing locator uses all four antenna nodes, or may use only thelower three to dynamically fit sensor data to a cylindrical field model.

Secondly, distortion defocusing (FIG. 23B) is used to display thequality of the fit.

An ongoing challenge in underground-utility-locating is to improve theaccuracy of each locate. The importance of accuracy in utility locationcannot be underestimated, as “hits” resulting from inaccurate locatestranslate into human injury, loss of life, and millions of dollars inlost revenue due to service interruptions. Improved accuracy can beaccomplished by aiding the operator in assessing the quality of the EMfield radiated from the buried utility being interrogated.

To mitigate inaccurate locates, the locator system presents the operatorwith a wide range of independent data including field strength, fieldangle difference between two antenna nodes with a linear offset, depthof radiator, and field gradient level. The operator must assimilate andanalyze this data to determine the quality and accuracy of a givenlocate. This requires a somewhat sophisticated physical understanding ofwhat the EM field radiated from the buried utility “looks like” and howit may be effected by objects in the vicinity of the locate.

This method simplifies the GUI for the operator by presenting a moreintuitive display representing the quality of the signal radiated fromthe buried utility. It unambiguously displays the “quality” of thesignal in an intuitive manner.

Past efforts to help operators assess the degree of field distortionrelied on displaying a representation of the measured field anglessensed by the top and bottom antenna nodes. An example of this prior artis seen in FIG. 23F. In FIG. 23F, a display mapping area 2508 shows atrace line 3106 as detected by the lower node of a two-node antennalocator, while a second line 3104 displays the trace line as detected bythe upper of the two nodes of the locator of FIG. 23D.

With such early displays, the user is expected to interpret angular andpositional differences in the two lines as a measure of fielddistortion. Unfortunately, the mere presence of a line drawn on thedisplay is enough to lead some operators into believing they havelocated the utility line sought, even though the top antenna node fieldangles reflected heavy distortion.

The direct-distortion display embodiment combines the field angleinformation that was previously displayed as two separate and distinctdisplays into a single visual indication that is both simpler and moreintuitive for the operator to interpret, and instantly reflects thequality of the locate to the operator unambiguously. FIGS. 23G-Jillustrate this novel interface and display in more detail. In FIG. 23G,a locate trace of relatively high certainty is illustrated in which thedefocusing radius is only 1. In FIG. 23H, with a higher distortionvalue, the radius is set to 3, and the display of dithering or blurringaround the line portrays a higher degree of distortion, or lowerconfidence. In FIG. 23I, the radius value is computed to be 10, with aproportionately wider distortion in the line display indicating acorrespondingly lower certainty in the locate. FIG. 23J illustrates theprocess carried further with a higher distortion value and the traceline 3114 in the display's mapping area 2508 showing proportionatelyless certainty.

There are two basic steps to this direct-distortion display method; (a)calculation of the level of field distortion present, and (b) generationof the visual indicator GUI display that represents the level of fielddistortion.

Estimation of Field Distortion: The degree of field distortion isdefined by the equation in FIG. 23 K, where θ is the measure of thevertical angle component of field angle and φ is the measure of thehorizontal angle component of the field.

Display of Field Distortion: Using the level of distortion calculated inthe equation in FIG. 23 K, a novel graphical display has beenimplemented to present the information in an intuitive manner. FIG. 23 Jillustrates a single instance of a random “point cloud” 3114. A pointcloud is defined by its center (x, y) coordinates, the radius of thepoint cloud, and the density of the point cloud. The center coordinatescorrespond to where the cloud originates on the graphical display. Theradius of the point cloud corresponds to the maximum distance, boundedto a square that a given point in the cloud can travel from the centercoordinates. The density of the point cloud corresponds to how manyindividual points appear in the point cloud. Given these input criteria,the coordinates for each point are generated using the Cpseudocoderoutine of FIG. 23L, where % is the Modulus operator. In practice,radius is set to be equal to the value of Distortion calculated asspecified by the equation in FIG. 23K. For the final output display,each point of the line representing the bottommost antenna nodes sensedfield angles is replaced with a point cloud, resulting in displays asseen in FIG. 23G through FIG. 23J described above.

Using a mapping locator embodiment, positional information may also beemployed to achieve the result described above. Using this techniquerequires that the data be spatially related so that the overall shape ofthe field from the pipe or cable can be ascertained from spaced apartmeasurements. This technique can be applied to distortion in a highlygeneral sense where the measured fields vary in some way from anexpected ideal field. Any calculation means to indicate some measure ordegree of variance from an ideal or expected field can be employed. Anydisplay means to graphically indicate uncertainty or ambiguity can beemployed.

The Locate Validation Method

Attention is now directed to FIG. 24A, which illustrates anotherembodiment wherein a locator is provided with a program element (FIG.27) to display visual indications alerting the operator when a locate iscertain enough to justify painting or marking the ground with thedetected utility line location, and when a locate is not certain enoughto “put down paint.”

FIG. 24A is a diagram illustrating an exemplary GUI display of adistorted single locate warning for signal properties showing anunacceptable locate result. In FIG. 24A, the display screen 2508 isshowing a sample message 2902 that the locator generates according tothe degree of calculated certainty of the reported location of a targetutility. Such a calculation is based on locator-processed signalstrength comparisons from the several antenna nodes. In an alternativeembodiment of this method, a color display may be used to displayparallel red lines indicating the “mis-mark allowance” or tolerance forerror in marking the ground to indicate the location of a utility,usually ±18-inches within the United States, or to display a similarpair of green lines to indicate the ±3-sigma confidence limits of thedetection, for example. When the green lines lay outside the red ones, avisual message such as “No Paint—Request Potholing” or the like can beused to advise the locator operator. This display embodiment, and othersextended on similar applications of this method, resolves a clearly-feltindustry-wide problem with locating errors resulting from under-trainedand under-experienced employees in a high-turnover industry. Theparameters of such a software program element can be adjusted toaccommodate geo-local variables for locators used in Europe or Asia, forexample.

FIG. 24B is a diagram illustrating an exemplary GUI display of aminimally distorted single locate message for signal properties yieldingan acceptable locate result. In FIG. 24B an “OK” message 3002 shows onthe display screen 2508 to confirm that the locate is of sufficientreliability to mark the utility's location on the ground. Such a displaymay be automatically generated during a locate, for example, when thealignment of multiple sensor information, depth calculation, signalstrength, and other calculations was such that a high certainty of agood locate was justified.

The Laser Range Finder Accessory

In another embodiment, the attachment is an optionally removable laserrange finding device that may measure distances by pointing to a targetor scanning across a target and calculating its nearest point. Theman-portable laser range finder 1820 may be operated while coupled to amapping locator in vertical orientation or held in a horizontalorientation, or it may be operated as a separate device as required bythe circumstances of use and task.

The following discussion provides further insight into the design,methods and techniques of the several embodiments of a laserrange-finder attachment that can be detached and deployed and/or used asa stand-alone device, illustrated in FIGS. 25A through 25M. According tothis embodiment, one or more dipole transmitters is fixed to aman-portable Laser Range Meter, and the self-standing, Multi-Channellocator is used to precisely establish the position and pointingdirection relative to the locator. The Laser Range Meter thenestablishes a distance from itself to some target point and thisinformation can be used to accurately establish the three dimensionalposition of this target point in relationship to the locator. The rangeinformation can be communicated from the man-portable laser range meterto the self-standing multi-channel locator by known means including,cable (USB, RS-232, etc.) or wireless radio (Bluetooth, Zigbee, WiFi,802.xx, etc.) means. This range information can also be encoded into thetransmitted dipole signal.

Collecting data with a laser range meter allows positional informationto be rapidly collected over a large area and also allows information tobe easily collected from practically inaccessible locations such as theposition of the top of a utility pole. Even wires strung between polescan be mapped if desired. Complex topography and objects hereto verydifficult to map become easy to map quickly in the field in real time.The self-standing locator may include program elements adapted to usethe techniques described by Rorden et al. in U.S. Pat. No. 4,710,708(entirely included herein by reference) to determine the position andorientation of the Laser Range Meter attached dipole(s) relative to theantenna array. In particular see FIGS. 25A-25B, or the sub-class systemtype 1.1 of Rorden et al. As described elsewhere herein and in one ormore of the commonly-assigned patent applications cited above and fullyincorporated by reference, the position of the self-standing locatorrelative to the world coordinate system may be established by variousmeans including GPS, compass, tilt sensors, inertial navigation and inparticularly fixed dipole transmitters or spinning dipoles in fixedlocations. One method is to embed into the laser range-finder a devicesuch as the AMI-601 described above.

The preferred embodiment uses a Laser Range Meter such as the HILTI PD28 that can stream range data continuously and measure from 0.1-100 mwith an accuracy of +/−3 mm at a 10 Hz rate (with normal reflectance).The Leica DISTO A3 is another suitable device if it is modified forremote data output. Other types of range meters, for example thoseemploying sonic pulses can also be used.

An audio signal may be employed with the laser range meter, associatingmeasured range with frequency, where close objects are associated with ahigh frequency audio signal and lower frequencies are associated withmore distant objects. This greatly improves the intuitive character ofthe tracing objects for the operator.

Several controls may be added to the range meter or any separate userinterface that may be associated with the use of the range meter. Onesuch control associates a line with two endpoints, which is useful intracing a curb edge or a utility pole. Another exemplary control is“trace area,” which can be used to trace a building or sign face forexample. Associating data points with known geometries simplifies thelater interpretation of the data collected and also makes real time mapcreation less ambiguous.

In a similar vein, audio annotations can be incorporated so the eachtraced object can be described or named as it is added to the mappingdata set. A Bluetooth headset such as used with cell phones is usefulfor such a purpose. Such audio annotations may be compressed and loggedinto an internal file structure or database by known means. Voicerecognition techniques may be employed to automate this process. Theuser may shoot a pair of points, one at the base of a utility pole andone at the top of the pole and then read the pole number off of a tag onthe pole itself. Tracing a circle around a manhole cover and then audiologging the statement “storm drain manhole cover” would make the mappingdata set more useful. Techniques using high Q dipoles to increase usefulrange and reduce power requirement can be employed to improve systemperformance as described elsewhere. Other techniques involvingsuspending a high Q resonant LC tanking to encode phase data can also beemployed to improve system performance. Such techniques can involvecomplete or fractional cycle skipping. The locator can employ long timeconstant digital filters of very narrow bandwidth to improve the signalto noise ratio of positional reference dipoles while it is placedunmoving an a self-standing configuration to improve mapping accuracyand range.

Various techniques can be used to resolve any laser pointing directionambiguity. Accelerometers may be placed on the range meter. A compassmay be placed on the range meter. Two dipoles may be employed to bothimprove positional and pointing accuracy but also to resolve anypointing direction ambiguity. Phase encoding techniques can also beemployed in the signal transmitted by the dipole to resolve pointingdirection. In areas where magnetic or conductive objects are likely tobe present it is desirable to use low frequency dipole beacons (1 Hz to10 kHz). With multiple beacons and the spaced apart antenna array of theself-standing locator the presence of distortions in the mapping signalscan be recognized and at least partially corrected for. The use of othernavigational sensors (GPS, optical, inertial) not based upon the dipoletransmitted fields are desirable in high distortion regions.

The laser range meter can be optionally mounted on a low cost scanningassembly, where for example, the laser may start pointing straight upand then rotate azimuthally around, while slowly scanning downwards inpolar angle thereby entirely scanning the region into which it isplaced. The scanning speed is a function of the maximum range and theresolution desired as well as the maximum update rate of the laser rangemeter. With constant and known rotation rates and with the geometry ofthe rotation device well characterized, the scanning accuracy of such anarrangement can be improved over that of free hand pointing. Automatedsoftware can more readily assemble the stream of data points into asurface model of the mapped region. As an example, the rotating devicemay itself be battery powered, and mounted or placed on top of theself-standing locator.

Triangulation techniques can be employed to accurately map larger areaswith a number of uniquely identified (e.g. numbered) laser targets.Electromagnetic dipole beacons are not needed if the locator does notneed to move during the mapping process (as would normally be neededwhen locating a buried utility). A utility can be located by moving thelocator and then the locator can be placed on the ground in aself-standing state and its position mapped by the following process.Two or more laser reflective targets (three to remove all positionalcrossing the baseline ambiguities) are placed in the area to be worked.These may be visibly marked with 1, 2, 3 or A, B, C, for example. Usinga sighting scope filtered to enhance laser beam visibility, the operatoris prompted to “shoot” all three targets in sequence each time thelocator is moved to a new location. A trigger action with sound oroptical feedback may be used to facilitate shooting each of thesetargets. As additional positions are “shot” an iterative procedure canbe used to generate a best fit position for all of the laser targets.The laser range meter should be relatively stable in position andorientation when it is being pointed at a target, so an accurateposition and orientation can be measured using the attached orintegrated sonde signal. A single dipole beacon may be placed at eachlaser range fixed position to allow fine scale mapping around thatlocation.

The basic problem of iteratively determining the unknown targetpositions from a series of range data sets is essentially identical tothe problem of establishing the positions of an acoustic transpondernetwork placed in the ocean. These techniques were refined by the DeepTow group at the Scripps Institution of Oceanography in the 1960's and1970's. Multiple self-standing locators can be used to simultaneouslysurvey and map a region. The data can be exchanged in real time betweenunits in the field via wireless means or the data can be time stampedwith local synchronized or GPS clocks and later processed into a singlemapped data set.

A low cost medium precision (1-10 cm) fast convenient surveyingtechnique is proposed using the self-standing locator and a trackeddipole transmitter attached to a hand-pointable laser range meter. In apreferred embodiment, the locator also includes a three axis electroniccompass and a three axis tilt-meter (3 axis accelerometer) so that itsorientation with respect to the earth's surface is known. A method ofusing “beach ball” or “lampshade” laser range meter reflectors totriangulate the position of the self-standing locator is described. Alaser target is constructed using a spherical shape of known radius witha reflective coating such as 3M Scotchlite (brand) Reflective SheetingMaterial, preferably red if a red laser is used. Using a square foot ofthis material, a HILTI PD 30 was able to give a range at 180 meters onan overcast day in San Diego. At ranges of less than 10 meters thereflected beam was too bright and a diffuse white band can serve toreflect the beam at closer ranges. A spherical reflector can be usedwhere the beam is aimed at the center of the target and moved for ashort period of time and the closest range is taken as the targetdistance. The known radius of the target is added to the measureddistance to get the distance to the centroid of the target. If rangingis mostly horizontal then “lampshade” targets are more suitable. Theselampshade targets are lower cost to produce than spherical targets andonly introduce small errors if the horizontal range is much greater thanany vertical offsets and if they are placed approximately at the heightof the laser range meter during measurement, such that the laser beam isnominally normal to the surface at the point where the cylindricalsurface is closest to the range meter. Each of these targets has someidentification means that the operator can use to indicate to the systemwhich target is being ranged at the time of range measurement.

A physically large target makes it easier to shoot the target with thelaser beam. A horizontally-oriented cylindrical strip can be searchedfor by the operator when sighting with vertical scanning movements andthen when the strip is found (laser return reflection visible), then thetarget can be scanned horizontally so that the minimum point can bemeasured and determined. The laser operates in a streaming mode, with aspring loaded trigger and sighting scope. Optionally a GPS receiver maybe placed in association with each laser target. While the trigger isdepressed the range meter streams measurements. The system has aninterface to allow the operator to indicate which fixed laser target isbeing ranged.

At shorter distances the vertical precision of the dipole tracked tiltmeasured during ranging provides an accurate elevation measurement. Atlonger ranges the triangulation of distance provides the desiredaccuracy.

Each set of range measurements (made with the locator at a fixedposition) to a target set is stored and referenced back to thecoordinate system of the locator (not the laser range meter at the timeof measurement). Measurements at subsequent locations allow the relativepositions of the targets to be determined by simple geometry and thenthe true relative position of the locator with respect to the array oftargets to be accurately determined. The basic geometric principle isthat the locator must lie on some circle equal in radius to the measureddistance to each target ranged. It is straightforward to start with thetargets in unknown locations and to determine the spacing and positionof the targets after the locator is moved to a small number of spacedapart locations within the area of the array of targets.

Several in use examples are herein described.

Example #1 Locating Utilities in a Road Intersection

A fixed positional reference dipole beacon is placed at each of fourcorners of an intersection, each transmitting a separatelydistinguishable signal that can be located by the self-standingmulti-channel locator. These positional reference dipole beacons canthemselves consist of one or more transmitting dipoles. Signals areplaced by known means (direct connection or inductive coupling) on allknown utilities within the region of the intersection to be mappedeither using separately distinguishable signals or by attaching signaltransmitting means to one utility at a time. Using both active (signalsplaced by the transmitting means) or passive (signals of opportunityalready present) locating techniques elsewhere described, the positionsof all detectable utilities are determined relative to the position ofthe locator at the time of measurement. The position of the locator isdetermined at the same time relative to one or more of the positionalreference dipoles. The locator collects and processes the signalsdetected from the various buried or otherwise hidden utilities anddetermines their positions relative to the intersection, and presents amap of these utilities on a display.

Additionally a high Q electronically spinning dipole can be employed asan omnidirectional inducer to couple signals onto unknown utilities inthe area. If the position of the dipole is accurately determined and thelocator's position relative to the inducing, spinning dipole source iscontinuously determined, then the measured signal can be subtracted fromthe computed value of the known signal and any residual is the inducedcomponent from some unknown utilities.

At any time during this locating and mapping process the operator canuse the “handpointable” laser range meter to add objects or any desiredreference points to the acquired map. Any objects present in the area ofthe intersection can be mapped to provide context for future excavationor construction activities and can help affirm the accuracy and utilityof a construction map that may be produced either immediately onsite orby later post processing. The laser range meter can be used to traceobjects such as poles, signs, curb edges, manhole covers, trees,buildings, fire hydrants etc. Objects can have height as well asposition that make the information more intuitive and allows a threedimensional map to be created.

Laser Range data accuracy will be improved if the portable locator isplaced unmoving on the ground in a self-standing state while the laserrange meter data is collected. For best accuracy, it is desirable tokeep the positional reference dipole transmitter attached to the laserrange meter close to the antenna array on the self-standing locator. Theoperator carries the locator from place to place within theintersection, sets the locator on the ground and then maps nearbyobjects and then repeats this procedure until all desired objects withinthe intersection area are mapped. The position of the locator isdetermined relative to the four beacons set at the intersection cornersand the position and orientation of the hand-pointable laser range meteris determined relative to the locator. Many communities prohibitnon-removable utility markings on the ground, so there is a need forrecording the position of all paint or flag markers that are placed. Therange meter can be used to trace all paint marks and record the precisepositions of any flag markers placed relative to any other known fixedobjects. Excavators have been known for example to remove flag marksbefore digging or to deliberately replace these in another position toplace blame on the locators if damage occurs during excavation. Theobject mapping capability as described herein provides means forauditing both the positional placement of located utilities and anyplaced markers.

A paint-less, electronically mapped method of marking utilities can beenvisioned whereby a detailed printed map of the intersection isprovided to the excavating contractor in lieu of painted marks on theroadway. In such case the relative position of buried utilities relativeto known, clearly distinguishable local landmarks and reference pointsis of critical importance. Alternatively, the amount of marking paintplaced onto the roadway may be greatly reduced and only a few referencemarks may need be employed to unambiguously tie the electronic map or aprinted facsimile thereof to known reference objects. If a self-standingmapping locator with a copy of the mapped information was present, thenexcavation and construction may use this electronic map in the field.

A key advantage to this process is that the construction activities suchas the position and depth of trenches, as well as any unmarked objectsencountered during construction can be easily added to the site map andeven transmitted in real time to some monitoring site or supervisor. Itis very fast and easy to place the self-standing locator next to apartially dug or completed trench and use the hand-pointable, laserrange meter to map all aspects of the trench and the position of any newor existing exposed utilities therein. Any information gathered by othertechniques disclosed elsewhere such as by GPR, and acoustic techniquescan of course be merged into any data set of mapping information.

Example #2 Mapping an Existing Structure and Site for RemodelConstruction

A number of high powered very low frequency beacons are placed externalto a structure. These beacons incorporate GPS receivers and use somecombination of DGPS, WAAS and RTK techniques to improve accuracy. Thefact that these are not moving during the course of the structuremapping process aids in improving the positional accuracy of thesedevices. The positional data from each of these beacons can betransmitted continuously or downloaded later to the self-standinglocator or some other data logging station. Some number of optionallylower power beacons, are placed temporarily through out the structure asneeded. The self-standing locator is moved from room to room or fromarea to area, and the hand-pointable laser range meter is then used tomap each area. The laser range meter may have controls that designatessuch measured values as floor, wall, and ceiling to aid automated ormanually directed means of assembling a map or CAD model or thestructure by known means. Other building components such as electrical,fire sprinkler, light switch, furniture etc. provide an additional levelof detail. These models typically consist of surfaces that can beconnected edge to edge. IGES or STL are file structures that may beemployed for this purpose.

These data may then be used to create CAD model of the structure thatallows new construction plans to be readily incorporated therein.

The width of access points can be readily determined so it can bedetermined to certain sizes of machinery (a Bobcat excavator forexample) can reach certain areas. Crane reach and access can bedetermined from such a model. The cubic feet of earth one needs to move(or remove) may be more accurately determined.

Example #3 Mapping Square Footage of a House for Resale Listing

Often the square footage of a house is not well known and may change dueto new construction. Such measurements are often not accurate and may bebiased from the seller's perspective. Either prior to listing or duringa home inspection period prior to close of escrow it may be desirable toaccurately verify the useable floor area of a structure. If an absolutemap is not needed this can be done with a single beacon or even noreference beacon or by using the beacon in the laser range meter itselfto determine the positional offset of the self-standing locator when itis moved from room to room.

Similar to the techniques described in example 2 above, the locator ismoved and placed, perhaps on a stand (to reduce distorting magneticcoupling to any nearby objects) in the middle of each room. Thehand-pointable, dipole tracked laser range meter is then used to map theroom, perhaps only the floor area. Often floor areas are cluttered withfurniture however so mapping the ceiling instead may be more desirable.Any ceiling tile is easily projected onto a floor surface that may betagged with a single point or alternately partly traced where notoccupied by furniture. Then the laser range meter may be placed at apoint intermediate between the current locator location and the nextpoint to which this it is going to be placed. A “move” action can besignaled by the operator or alternately accelerometers in the locatorand or the range meter can be used to automate the move of the locator.During the move the range meter is assumed to be fixed and the locatoris moving. This process is repeated until the floor area of the house ismeasured.

Example #4 Mapping for Carpet Installation within a Building

This activity is very similar to that described in example #3 above.However when laying carpet it is important to know maximum widths andshapes to be able to determine the width, length and numbers of rolls ofcarpet needed to complete the job. Software can be developed to providean exact optimal description of how the carpet should be installed,largely automating job quoting and the design of each installation.

Example #5 Tree Trimming Mapping

All of the (not occluded by foliage) major branches of a tree can betraced from one or more positions beneath the tree. A trimming plan maybe developed and presented to a landscape artist or a prospectivecustomer. Models for developing a lighting plan for landscaping may bedeveloped.

Example #6 Using a Large Number of Small Lower Powered Simple DipoleBeacons

A small “swarm” of dipole beacons may be used to map an area. If thelocator is close to several beacons at the same time accuracy isimproved and then either a beacon or the locator can be moved and therelative positions of the various system components (beacons andlocators).

If the information recorded in each locator is time stamped than severallocators can be used simultaneously to map an area.

Dipole beacons may all run at a single frequency and be phase coded bysuspending an LC tank by some fractional cycle in a time coded manner.

Example #7 Horizontal Directional Drilling (HDD) Site Survey andMonitoring During the Drilling Operation

An array of laser target reflectors is used to map the position of theself-standing locator as it is moved from point to point approximatelyalong the propose and or actual drill path. The absolute position of thedrill head is dipole tracked.

Returning now to FIG. 25A a perspective view is shown of a man-portablelaser range finding device 1820 showing a first dipole beacon 1824, asecond dipole beacon 1826, a wireless communication means 1832, and thelaser beam 1828. Also shown is a cutaway in FIG. 25A are an embeddedcompass 1831 and tilt sensor 1833. The particular locations of thesecomponents is exemplary only. As shown in FIG. 25A, the device may beoperated independent of the locator, for laser-ranging by hand or from afixed location separate from the locator 102. It may also be used whileattached to the accessory mounting interface by lifting the locatoruntil the range finder is level with the ground, for example, orattached to the upper shaft of a self-standing locator for takingbearing and range measurements.

The two distinguishable dipole coils 1824 and 1826, enable the locator102 to fix the relative position of the laser range finder. Optionally,a third coil 1830, built into the laser range finder such that its fieldis coaxial with the laser beam itself, facilitates an orientationcalculation in any mapping process including the laser range finder'sinformation. If the signal from the coaxial-coil field is subjected tocycle-skipping techniques as described above, it serves to provideorientation information for the hand-held laser range finder itself. Theside-coils and the co-axial coil can be attached in combination orseparately to an embodiment of the laser range finder device, forexample.

Turning now to FIG. 25B, a front view is given of the locator 102 fromFIG. 3 in an open disposition for operation with the accessory mountinginterface (104, not shown) coupled to an exemplary laser range findingaccessory embodiment. In FIG. 25B the laser range finding device isattached to the locator by means of the accessory mounting interface. Itmay measure distance to ground directly beneath it, or scan to eitherside, as indicated by lines 1812, 1814, 1816, as examples. In FIG. 25Bthe antenna node 108 behind the laser range finder attachment is shownghosted (in dashed lines) for clarity of illustration. Two dipole beaconunits 1824, 1826 can be seen attached to either side of the man-portablelaser range finder 1820.

A wireless communication link, such as Bluetooth, 802.11 or Zigbee forexample, or a coil-cord extension cable may similarly be built into therange finder attachment enabling it to exchange data with the locator102 or any other similarly equipped peripheral of the system. In ahand-held laser device so configured, such as with two pill sondessurrounding a laser pointer, linked via Bluetooth, for example, to thelocator, three-dimensional mapping of any environment may be done merelyby pointing and activating a logger for points of interest, including,for example, curbs, manhole covers, hydrants, lampposts and similarartifacts, survey medallions, past or present paint marks on pavement,enabling the locator to map with precision where each target point is inthree-dimensional space. A GPS unit may be incorporated into such alaser-pointing device to augment its objective location information. AZigbee interface, for example, enables the device to permitvoice-logging of information for targeted points in the mappedenvironment. Reference points during a line trace operation maysimilarly be logged. Note that with two sondes of different frequencies(or otherwise distinguishable by the locator) being detected by themapping locator, the relative location and orientation of the laserpointer is constantly known to the locator. This assumes that the rangefinder is not held in an inverted position. An integrated AMI-601 chip(as discussed with the accessory mounting interface disclosure) in thelaser range finder would equip it as well to provide compass andaccelerometer information in the locating process.

Turning now to FIG. 25C a scenario is depicted in which a target formapping purposes is selected, in this case a traffic sign, and the laserrange finder is employed as a hand-held device to determine a range tothe target. Communication with the locator 102 is maintained by wirelesslink, and the relative location of the hand-held laser range finder ismonitored by the locator 104, which senses and measures the fieldstrength of the dipole beacons attached to the range finder. In analternative configuration the laser range finder may be mounted by aclip to the shaft 1840 of the locator for ranging on targets with thelocator in a fixed location, for example. As discussed earlier, thelocator maintains information concerning the relative position of thelaser range finder, which in turn detects the relative position of thetarget. Given relative distances D_(T) and D_(LR), and the anglesindicated as θ and ψ, the precise location of the target traffic signcan be computed.

In a further adaptation of this accessory, attention is now directed toFIGS. 25J and 25K, each of which depicts a moveable target for use inlaser range finding. The basic configuration of the target consists ofan upper target 3202, a visual identification number in large lettering3206, an optional lower target 3204, and a stand, here shown as anadjustable tripod. As shown in FIG. 25K, one configuration of the targetmay be in the illustrated “lamp shade” form in which the targets are oneor more cylindrical sections disposed vertically. In the lamp shadeform, a section of each cylinder has a reflective surface, such as maybe provided by red Scotchlite tape or some equivalent surfacing. Theother portion of each cylinder is surfaced in some reflective whitesurface more suited for close-range laser ranging. In an alternativeembodiment, the target segments may be reflective spheres, here referredto as the “beach ball” form. When more than one cylinder or ball isused, the distance between the segments is a known measured distance. Itshould be emphasized that only one reflective cylinder or ball isrequired, but that with two targets of a known separation, improvedaccuracy in determining relative height can be achieved. In practice,the device being used, such as the locator or range finder, needs to beinformed of which target is being selected. This can be achieved througha key pad on the range finder, through a microphone with voice I/O, orthrough incorporating a dipole beacon or other embedded identifier intothe target that may be recognized by the locator used in conjunctionwith the range finder. In use, the beam from the range finder is sweptacross the target and the minimum distance value to the target isrecorded. If a single reflective cylinder or sphere configuration isused, a compensation for any tilt in the laser range finder should alsobe incorporated in the calculation of distance. This may be achieved,for example, by comparing the location characteristics of the two dipolebeacons attached to the range finder, by the use of an embeddedtilt-meter or multi-axis accelerometer, or by other means.

An example of the “beach ball” form of reflective target is shown inFIG. 25D, to which attention is now directed. In FIG. 25D a “beach ball”target consisting of two reflective spheres, 3402 and 3404, verticallydisposed, with a visual identification marker 3206, are deployed.Further in FIG. 25D, two laser range measurements R₁ and R₂ are shown inone exemplary application as being taken from the location of a locator3408 (Position A). Two more readings by laser range finder from FIG. 25Ameasuring R₃ and R₄ are shown being taken in connection with a locator3410 at Position B. The locators may be separate devices or the samelocator may be moved from A to B for readings. The range finder may bewired, hard-coupled, or linked by wireless to the locator. Multiplerange finders may be used, or a single device may be moved for a seriesof readings. As shown in FIG. 25D, from the measurements provided by therange finder readings, the relative vertical measurements Z_(A) andZ_(B), corresponding to the two down-slope locations A and B, may becalculated. When a pair of vertically disposed or stacked targets isused, the accuracy of the vertical component of measurement increases asthe known distance between the two targets. This known distance providesthe basis for independently measuring or calculating the relative heightof the laser, reducing any variability caused by tilt in the rangefinder. The locator 3408, 3410 used in conjunction with the rangefinder, or other computational device used, must know which measurementis associated with the upper target 3402, and which with the lowertarget 3404.

Turning now to FIG. 25E, another application of the laser range finderis shown. In FIG. 25E, a “beach ball” target form is shown and a laserrange finder from FIG. 25A is shown in two instantiations, 3508A and3508B measuring polar angles θ₁ and θ₂ for the elevation of the twoballs 3202, 3204, and distances 3502 and 3504. From the measurement ofangle θ₁ and θ₂ and ranges 3502 (R_(upper)) and 3504 (R_(lower)) it ispossible to calculate the elevation T_(E1), given a known distancebetween the two balls T_(H1).

Attention now being directed to FIG. 25F, an extension of the foregoingprinciples can be shown, illustrated in a view from above, of a locator3606 that is determining a bearing on a target 3602. The target in thisinstance may be equipped with a dipole beacon built into it enabling thelocator 3606 to measure its distance and bearing by means of itsomnidirectional antennas. At the same time a man-portable laser rangefinder 3604 as shown in FIG. 25A, may take a bearing on the same target3602 from a distance from the locator and communicate its measurementsby a wireless data link, including data from an embedded compass andtilt sensor in this embodiment. By correlating the data from the laserrange finder 3604 with its own measurements, the locator may translateits local coordinate measurements into the target's real-worldcoordinate system (X_(t), Y_(t)) and report its own location and that ofthe target 3602. The radius of the target R(t) is known and is takeninto account in position calculation. If the coordinates (X_(LR),Y_(LR)) and orientation (Θ) of the range finder relative to the locatoris established by use of a dipole beacon in the range finder, then asingle compass in either the locator or the range finder provides enoughinformation to translate to a real-world coordinate system.Alternatively, both devices can include a compass. The use of at leastone compass facilitates coordinate solutions over distances too greatfor locator detection of the dipole beacons.

Turning now to FIG. 25G, a similar application is illustrated inresolving baseline ambiguity between two targets, here illustrated as3704 and 3706. Because locator 3702 is equipped with an electroniccompass it can determine angle Θ by comparing the compass bearinginformation with bearing information based on the dipole antennalocation of the beacon in Target 3704 and Target 3706. In this scenarioboth targets are equipped with a dipole beacon, and the laser rangefinder is coupled to the locator 3702 through the accessory mountinginterface, or alternatively mounted on the shaft of the locator. Thecombination of local coordinates and compass bearing information enableslocator 3702 to calculate real-world bearing and distance values for thebaseline between the targets. In an alternative embodiment, one or bothtargets may be equipped with a GPS receiver as well as a dipole beacon,allowing complete real-world coordinates to be determined for bothtargets and locator. In using dipole beacons, the local signal strengthof each dipole beacon can be measured at its source and transmitted overa wireless link to the locator for comparison. Either the comparison ofdipole beacon signal strength readings, or the laser ranging data, orboth, can be used in determining distances to targets.

As shown in FIG. 25G, the use of compass data in conjunction withdistance information can resolve, by triangulation using the compassangle Θ, the ambiguity as to which side of the baseline the locator ison at the time of measurement. Such a system is also useful with asingle-node antenna locator. If a multi-node antenna locator is used,the signal differences between the antenna nodes can be used in asimilar way to resolve the ambiguity. In the absence of compassazimuthal data associated with range measurements made, the system mustknow the distances between the targets (i.e., the length of thebaseline). This distance can be measured directly, or may beextrapolated in post-processing given sufficient data.

Similarly, turning now to FIG. 25H, a locator 3802 can determine localcoordinates by use of the laser range finder determining range andbearing to three targets (T₁, T₂, and T₃) 3808, 3806, and 3810, thusdefining three corresponding radii (R₁, R₂, and R₃). By rotating thesevalues based on compass and tilt corrections provided by the on-boardcompass and accelerometer, the locator 3802 is able to determine localglobal coordinates and translated radii X_(r), Y_(r), relative tocompass North. Provided with three ranges to three targets, theambiguity of the baseline can be resolved—that is, the location of thelocator relative to the targets can be determined unambiguously. Theradius of the target structure R(t) is known and is taken into accountin position calculation. In this scenario, each target can also containa low- to medium-powered dipole beacon or sonde, which should enable thedistance from any target to the other two to be known by comparison ofsignal strengths at the locator.

FIG. 25I is a graphical illustration of a method using three lasertargets such as shown in FIG. 25L below, and two locators of the typeshown in FIG. 25B to determine the relative locations of three targets.One locator, alternatively, can acquire the data serially from twolocations. In FIG. 25I, three targets 4110, 4106, and 4108 (T₁, T₂, andT₃) are shown with a locator at two locations (A, B) 4104 and 4102.Ranging information may be taken at location A using the laser rangefinder attachment measuring to each target. Moving the locator toLocation B, a second set of range values to each target may bedetermined. By comparing these range sets to the compass bearing, thelocator is able to calculate X_(T1), Y_(T1), X_(T2), Y_(T2), X_(T3) andY_(T3) in local world coordinates relative to A and B. Given a GPSreading from one or more targets, the complete real-world coordinatesmay be established. If compass information is included, only one targetneeds to be visible from any one location.

FIG. 25L illustrates an alternative embodiment of the “lamp shade” lasertarget equipped with a dipole beacon 3906 in which the red reflectivesegment 3902 and the white reflective segment 3904 of a singlecylindrical “lampshade” target are identified. A “beach ball” typereflector can be used equally well.

FIG. 25M illustrates an alternative embodiment of the same device, inwhich part of the target area is surfaced with a red reflective surface3902 such as Scotchlite, while the remainder 3904 is surfaced with areflective white surface for closer-range work. In FIG. 25M, a Target ID3206 consists of a large-print number, readable from a distance, ismounted below the actual target area on a vertical shaft that optionallymay be of a telescoping design. The shaft supports as well a shell 4002that contains an optional GPS sensor and antenna, an optional dipolebeacon, or both. Alternatively the dipole beacon may be separatelyplaced such as 3906. The shaft is mounted on a tripod formation 3908,which is hinged so that it may be collapsed for portability. In use, thelaser beam from a laser range finder 4004 is reflected from a portion ofthe target and the nearest distance to the target is computed.

The identification of a specific target can be automated by equippingeach target with an optical sensing means such that when the laser beamhits some predetermined part of the target the laser beam is sensed anda “hit” signal is sent by the wireless means to either locator 3606 orlaser range finder 3604 (FIG. 25F) so that a specific target can beidentified as the one the laser is pointing at. Any portion of thetarget can be made with an optically translucent and diffuse materialand a modulation of the laser beam may be easily detected by known meansby a light sensor mounted therein.

The Integrated Layer Display Device

FIG. 26 is a graphic illustration of one embodiment of the remotedisplay device in which geo-coordinated information from differentdevices may be assembled into layers for the enhancement of operatorinformation, later analysis or other requirements of operation. By wayof example, in FIG. 26, the display device is a laptop computer 4204coupled by wireless data link to locator 102. Data from one or morelocators and peripherals is integrated on the display 4204. The displayin FIG. 26, as an example, is integrating a layer 4208 of sonicdetections from the Leak Detection attachment, a layer 4210 of laserranging information, and a layer 4206 of EMF field detection informationbased on the omnidirectional antenna sensors. The layers aregeo-coordinated based on real-world coordinates that are calculated ordirectly measured from GPS capabilities built in to the severalattachments. The display device may be coupled to the locator bywireless link 4202 or by a wired connector. Layers may be selectivelydisplayed or hidden by the operator, and may be transmitted by thedisplay device to an office computer for further analysis andsynchronization with other maps or GIS databases.

FIG. 27 is a schematic block diagram illustrating the relationshipsbetween the functional electronic elements of the locator system 102(FIGS. 1-3). Portions of the following description may be betterappreciated with reference to the commonly-assigned patent referencescited above and fully incorporated herein. A plurality of EM sensorarrays 2704 provide analog signals 2706 to the analog-to-digitalconverters 2708, which produce digital signals 2710 representing theB-fields at sensors 2704. A signal processor 2712 accepts B-fieldsignals 2710 and produces a filtered B-field gradient signal 2714representing a specific B-field component of interest at sensors 2704.In the example shown, B-field filtered signal 2714 is transferredthrough memory 2716 to the locator processor 2718 for use in developingsignals representing target locations that may be combined with othersignals internally by locator processor 2718 to produce and transfertarget location signals on the bus 2720 to the user interface (UI)processor 2722, which generates the appropriate visual and aural userinterface signals for display on the GUI 2724 and for reproduction atthe audio user interface 2726. An optional keyboard 2728 is disposed toaccept commands from the user for transfer to locator processor 2718 byway of user interface processor 2722 in the example shown.Alternatively, keyboard 2728 may be embodied as a touch-sensitive screenoverlying GUI 2724, for example. Finally, a wireless port 2729 iscoupled to the user interface processor to permit the locator system 102to exchange commands and data with any other similarly equipped locatorsystem or any remote host computer equipped to communicate through thewireless port 2729. Alternatively, wireless port 2729 may be embodied asany other useful network or data port adapted for such purposes. As usedherein, the term “processor” can refer to a hardware device or simply asoftware component.

An important feature of the locator system embodiment 102 is theadditional capability for integrating and processing signals from any ofa predetermined group of accessory sensor systems by means of theaccessory mounting interface 2730. The selected accessory 2732 iscoupled to accessory mounting interface 2730 by means of a temporaryelectromechanical coupler 2734 having a mechanical accessory mountinginterface coupler and an electrical accessory mounting interfaceconnector adapted to transfer electronic signals and electrical power onthe bus 2736 between accessory system 2732 and, in the example shown, anaccessory signal processor 2738. Accessory processor 2738 includes aplurality of program elements, exemplified by the GPR program element2740, adapted to control and process data from a particular one of thepredetermined accessory sensor system group, exemplified by the GPRsensor system described above. Alternatively, some or all of the GPRprogram element 2740 may cooperate with (over the data bus 2742) or beembodied as a program element 2744 within the locator processor 2718,for example. Finally, in addition to the accessory sensor systemsadapted for temporary coupling at accessory mounting interface 2730, theinertial and GPS sensing circuit 2746 is preferably fixed within one ofthe EM sensor arrays (e.g., sensor array 106 in FIGS. 1-3). In theexample shown, on the data bus 2748 to locator processor 2718, sensingcircuit 2746 provides an electronic signal corresponding to thehorizontal orientation of the locator system from a compass circuit (C),an electronic signal corresponding to the vertical orientation of thelocator system from a tilt-meter circuit (T), an electronic signalcorresponding to changes in the locator system orientation from anaccelerometer circuit (A); and an electronic signal corresponding to theGPS coordinates from a Global Positioning System (GPS) receiver circuit(G). Of course, these four signals on bus 2748 may be provided by anyuseful arrangement of discrete elements or other combinations ofelements, and one or more signals may be omitted for convenience.

Clearly, other embodiments and modifications of this invention may occurreadily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

1. A human-portable locator system for locating a buried objectcharacterized by an electromagnetic (EM) field emission having afrequency range centered at f₀ that also includes a jamming frequencyf_(J) wherein |f_(J)−f₀|=Δf≠0, the system comprising: an EM sensorarray; a gradient processing circuit coupled to the EM sensor array forproducing a target signal representing the B-field gradient at the EMsensor array as a function of time within a frequency range centered atf₀; and means for shifting the frequency passband of the gradientprocessing circuit away from jamming frequency f_(J) by an incrementf_(S)<Δf, thereby increasing the ratio of the target signal to thejamming signal.
 2. The system of claim 1 further comprising: a locatorprocessor coupled to the gradient processing circuit for producingsignals representing target locations responsive to signals acceptedfrom the gradient processing circuit.
 3. The system of claim 1 furthercomprising: a user interface coupled to the locator processor foraccepting user commands and for indicating the buried object locationrelative to the locator system.
 4. The system of claim 1 furthercomprising: an accessory mounting interface coupled to the locatorprocessor and disposed to accept temporary attachment of an accessorysensor system.